Image encoding/decoding method and apparatus, and recording medium storing bitstream

ABSTRACT

An image encoding/decoding method and apparatus are disclosed. The method of decoding an image according to the present invention, comprises, obtaining a single stream including subpicture information of a plurality of subpictures; selecting a subpicture to be extracted from among the plurality of subpictures; determining the single stream as a stream to be extracted and obtaining a sub stream for the subpicture to be extracted from the stream to be extracted, by removing or using at least one piece of subpicture information included in the stream to be extracted.

TECHNICAL FIELD

The present invention relates to a method and apparatus forencoding/decoding an image and apparatus, and a recording medium forstoring a bitstream.

BACKGROUND ART

Recently, the demand for high resolution and quality images such as highdefinition (HD) or ultra-high definition (UHD) images has increased invarious applications. As the resolution and quality of images areimproved, the amount of data correspondingly increases. This is one ofthe causes of increase in transmission cost and storage cost whentransmitting image data through existing transmission media such aswired or wireless broadband channels or when storing image data. Inorder to solve such problems with high resolution and quality imagedata, a high efficiency image encoding/decoding technique is required.

There are various video compression techniques such as an interprediction technique of predicting the values of pixels within a currentpicture from the values of pixels within a preceding picture or asubsequent picture, an intra prediction technique of predicting thevalues of pixels within a region of a current picture from the values ofpixels within another region of the current picture, a transform andquantization technique of compressing the energy of a residual signal,and an entropy coding technique of allocating frequently occurring pixelvalues with shorter codes and less occurring pixel values with longercodes.

DISCLOSURE Technical Problem

An object of the present invention is to provide an imageencoding/decoding method and apparatus with improved compressionefficiency.

Another object of the present invention is to provide an imageencoding/decoding method and apparatus by using subpicture merging.

Another object of the present invention is to provide an imageencoding/decoding method and apparatus by using sub stream extraction.

Another object of the present invention is to provide a recording mediumfor storing a bitstream generated by an image encoding/decoding methodor apparatus according to the present invention.

Technical Solution

The method of decoding an image according to the present disclosure,method comprising: obtaining a single stream including subpictureinformation of a plurality of subpictures; selecting a subpicture to beextracted from among the plurality of subpictures; determining thesingle stream as a stream to be extracted and obtaining a sub stream forthe subpicture to be extracted from the stream to be extracted, byremoving or using at least one piece of subpicture information includedin the stream to be extracted.

wherein the subpicture information comprises a non-video coding layer(VCL) network abstraction layer (NAL) unit and a VCL NAL unit for theplurality of subpictures.

wherein the sub stream is obtained by removing a VCL NAL unit for asubpicture which is not the subpicture to be extracted.

wherein the subpicture information comprises at least one of sequenceparameter set (SPS) information or picture parameter set information(PPS).

wherein the sub stream is obtained, by setting top left coding tree unit(CTU) coordinates of the subpicture to be extracted are set to (0, 0).

wherein the unchanged subpicture information comprises at least one ofinformation indicating whether to treat a subpicture as a picture,filtering information or subpicture ID information.

wherein the sub stream is obtained by removing subpicture informationfor a subpicture which is not the subpicture to be extracted.

wherein the subpicture information comprises at least one of a videoparameter set (VPS) NAL unit, an end of bitstream (EOB) NAL unit, anaccess unit delimiter (AUD) NAL unit or a supplemental enhancementinformation (SEI) NAL unit, and wherein at least one of the VPS NALunit, the EOB NAL unit, the AUD NAL unit or the SEI NAL unit is notremoved from the stream to be extracted.

The method of encoding an image according to the present disclosure,method comprising: obtaining a single stream including subpictureinformation of a plurality of subpictures, selecting a subpicture to beextracted from among the plurality of subpictures, determining thesingle stream as a stream to be extracted and obtaining a sub stream forthe subpicture to be extracted from the stream to be extracted, byremoving or using at least one piece of subpicture information includedin the stream to be extracted.

wherein the subpicture information comprises a non-video coding layer(VCL) network abstraction layer (NAL) unit and a VCL NAL unit for theplurality of subpictures.

wherein the sub stream is obtained, by removing a VCL NAL unit for a subpicture which is not the subpicture to be extracted.

A computer-readable recording medium having stored therein a sub streamreceived by an image decoding apparatus and used to reconstruct acurrent block included in a current picture, the sub stream beinggenerated by an image encoding method, the image encoding methodcomprising: obtaining a single stream including subpicture informationof a plurality of subpictures, selecting a subpicture to be extractedfrom among the plurality of subpictures, determining the single streamas a stream to be extracted and obtaining a sub stream for thesubpicture to be extracted from the stream to be extracted, by removingor using at least one piece of subpicture information included in thestream to be extracted.

Advantageous Effects

According to the present invention, it is possible to provide an imageencoding/decoding method and apparatus with improved compressionefficiency.

According to the present invention, it is possible to provide an imageencoding/decoding method and apparatus by using subpicture merging.

According to the present invention, it is possible to provide arecording medium for storing a bitstream generated by an imageencoding/decoding method or apparatus according to the presentinvention.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration of an encodingapparatus according to an embodiment to which the present invention isapplied.

FIG. 2 is a block diagram showing a configuration of a decodingapparatus according to an embodiment and to which the present inventionis applied.

FIG. 3 is a view schematically showing a partition structure of an imagewhen encoding and decoding the image.

FIG. 4 is a view showing an intra-prediction process.

FIG. 5 is a diagram illustrating an embodiment of an inter-pictureprediction process.

FIG. 6 is a diagram illustrating a transform and quantization process.

FIG. 7 is a diagram illustrating reference samples capable of being usedfor intra prediction.

FIG. 8 is a view illustrating an image coding/decoding method accordingto an embodiment of the present disclosure.

FIG. 9 is a view illustrating another image coding/decoding methodaccording to an embodiment of the present disclosure.

FIG. 10 is a view illustrating a subpicture included in one picture.

FIG. 11 is a view illustrating a stream including a plurality ofsubpictures.

FIG. 12 is a view illustrating a stream structure of a sub pictureaccess unit (AU).

FIG. 13 is a view illustrating a syntax element structure of an AUD.

FIGS. 14 and 15 are views illustrating a stream structure of a pictureAU.

FIG. 16 is another view illustrating a stream structure of a picture AU.

FIG. 17 is a view illustrating an example of merging sub streams togenerate a single stream.

MODE FOR INVENTION

A variety of modifications may be made to the present invention andthere are various embodiments of the present invention, examples ofwhich will now be provided with reference to drawings and described indetail. However, the present invention is not limited thereto, althoughthe exemplary embodiments can be construed as including allmodifications, equivalents, or substitutes in a technical concept and atechnical scope of the present invention. The similar reference numeralsrefer to the same or similar functions in various aspects. In thedrawings, the shapes and dimensions of elements may be exaggerated forclarity. In the following detailed description of the present invention,references are made to the accompanying drawings that show, by way ofillustration, specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to implement the present disclosure. Itshould be understood that various embodiments of the present disclosure,although different, are not necessarily mutually exclusive. For example,specific features, structures, and characteristics described herein, inconnection with one embodiment, may be implemented within otherembodiments without departing from the spirit and scope of the presentdisclosure. In addition, it should be understood that the location orarrangement of individual elements within each disclosed embodiment maybe modified without departing from the spirit and scope of the presentdisclosure. The following detailed description is, therefore, not to betaken in a limiting sense, and the scope of the present disclosure isdefined only by the appended claims, appropriately interpreted, alongwith the full range of equivalents to what the claims claim.

Terms used in the specification, ‘first’, ‘second’, etc. can be used todescribe various components, but the components are not to be construedas being limited to the terms. The terms are only used to differentiateone component from other components. For example, the ‘first’ componentmay be named the ‘second’ component without departing from the scope ofthe present invention, and the ‘second’ component may also be similarlynamed the ‘first’ component. The term ‘and/or’ includes a combination ofa plurality of items or any one of a plurality of terms.

It will be understood that when an element is simply referred to asbeing ‘connected to’ or ‘coupled to’ another element without being‘directly connected to’ or ‘directly coupled to’ another element in thepresent description, it may be ‘directly connected to’ or ‘directlycoupled to’ another element or be connected to or coupled to anotherelement, having the other element intervening therebetween. In contrast,it should be understood that when an element is referred to as being“directly coupled” or “directly connected” to another element, there areno intervening elements present.

Furthermore, constitutional parts shown in the embodiments of thepresent invention are independently shown so as to representcharacteristic functions different from each other. Thus, it does notmean that each constitutional part is constituted in a constitutionalunit of separated hardware or software. In other words, eachconstitutional part includes each of enumerated constitutional parts forconvenience. Thus, at least two constitutional parts of eachconstitutional part may be combined to form one constitutional part orone constitutional part may be divided into a plurality ofconstitutional parts to perform each function. The embodiment where eachconstitutional part is combined and the embodiment where oneconstitutional part is divided are also included in the scope of thepresent invention, if not departing from the essence of the presentinvention.

The terms used in the present specification are merely used to describeparticular embodiments, and are not intended to limit the presentinvention. An expression used in the singular encompasses the expressionof the plural, unless it has a clearly different meaning in the context.In the present specification, it is to be understood that terms such as“including”, “having”, etc. are intended to indicate the existence ofthe features, numbers, steps, actions, elements, parts, or combinationsthereof disclosed in the specification, and are not intended to precludethe possibility that one or more other features, numbers, steps,actions, elements, parts, or combinations thereof may exist or may beadded. In other words, when a specific element is referred to as being“included”, elements other than the corresponding element are notexcluded, but additional elements may be included in embodiments of thepresent invention or the scope of the present invention.

In addition, some of constituents may not be indispensable constituentsperforming essential functions of the present invention but be selectiveconstituents improving only performance thereof. The present inventionmay be implemented by including only the indispensable constitutionalparts for implementing the essence of the present invention except theconstituents used in improving performance. The structure including onlythe indispensable constituents except the selective constituents used inimproving only performance is also included in the scope of the presentinvention.

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. In describingexemplary embodiments of the present invention, well-known functions orconstructions will not be described in detail since they mayunnecessarily obscure the understanding of the present invention. Thesame constituent elements in the drawings are denoted by the samereference numerals, and a repeated description of the same elements willbe omitted.

Hereinafter, an image may mean a picture configuring a video, or maymean the video itself. For example, “encoding or decoding or both of animage” may mean “encoding or decoding or both of a moving picture”, andmay mean “encoding or decoding or both of one image among images of amoving picture.”

Hereinafter, terms “moving picture” and “video” may be used as the samemeaning and be replaced with each other.

Hereinafter, a target image may be an encoding target image which is atarget of encoding and/or a decoding target image which is a target ofdecoding. Also, a target image may be an input image inputted to anencoding apparatus, and an input image inputted to a decoding apparatus.Here, a target image may have the same meaning with the current image.

Hereinafter, terms “image”, “picture, “frame” and “screen” may be usedas the same meaning and be replaced with each other.

Hereinafter, a target block may be an encoding target block which is atarget of encoding and/or a decoding target block which is a target ofdecoding. Also, a target block may be the current block which is atarget of current encoding and/or decoding. For example, terms “targetblock” and “current block” may be used as the same meaning and bereplaced with each other.

Hereinafter, terms “block” and “unit” may be used as the same meaningand be replaced with each other. Or a “block” may represent a specificunit.

Hereinafter, terms “region” and “segment” may be replaced with eachother.

Hereinafter, a specific signal may be a signal representing a specificblock. For example, an original signal may be a signal representing atarget block. A prediction signal may be a signal representing aprediction block. A residual signal may be a signal representing aresidual block.

In embodiments, each of specific information, data, flag, index, elementand attribute, etc. may have a value. A value of information, data,flag, index, element and attribute equal to “0” may represent a logicalfalse or the first predefined value. In other words, a value “0”, afalse, a logical false and the first predefined value may be replacedwith each other. A value of information, data, flag, index, element andattribute equal to “1” may represent a logical true or the secondpredefined value. In other words, a value “1”, a true, a logical trueand the second predefined value may be replaced with each other.

When a variable i or j is used for representing a column, a row or anindex, a value of i may be an integer equal to or greater than 0, orequal to or greater than 1. That is, the column, the row, the index,etc. may be counted from 0 or may be counted from 1.

Description of Terms

Encoder: means an apparatus performing encoding. That is, means anencoding apparatus.

Decoder: means an apparatus performing decoding. That is, means andecoding apparatus.

Block: is an M×N array of a sample. Herein, M and N may mean positiveintegers, and the block may mean a sample array of a two-dimensionalform. The block may refer to a unit. A current block my mean an encodingtarget block that becomes a target when encoding, or a decoding targetblock that becomes a target when decoding. In addition, the currentblock may be at least one of an encode block, a prediction block, aresidual block, and a transform block.

Sample: is a basic unit constituting a block. It may be expressed as avalue from 0 to 2^(Bd)-1 according to a bit depth (B_(d)). In thepresent invention, the sample may be used as a meaning of a pixel. Thatis, a sample, a pel, a pixel may have the same meaning with each other.

Unit: may refer to an encoding and decoding unit. When encoding anddecoding an image, the unit may be a region generated by partitioning asingle image. In addition, the unit may mean a subdivided unit when asingle image is partitioned into subdivided units during encoding ordecoding. That is, an image may be partitioned into a plurality ofunits. When encoding and decoding an image, a predetermined process foreach unit may be performed. A single unit may be partitioned intosub-units that have sizes smaller than the size of the unit. Dependingon functions, the unit may mean a block, a macroblock, a coding treeunit, a code tree block, a coding unit, a coding block), a predictionunit, a prediction block, a residual unit), a residual block, atransform unit, a transform block, etc. In addition, in order todistinguish a unit from a block, the unit may include a luma componentblock, a chroma component block associated with the luma componentblock, and a syntax element of each color component block. The unit mayhave various sizes and forms, and particularly, the form of the unit maybe a two-dimensional geometrical figure such as a square shape, arectangular shape, a trapezoid shape, a triangular shape, a pentagonalshape, etc. In addition, unit information may include at least one of aunit type indicating the coding unit, the prediction unit, the transformunit, etc., and a unit size, a unit depth, a sequence of encoding anddecoding of a unit, etc.

Coding Tree Unit: is configured with a single coding tree block of aluma component Y, and two coding tree blocks related to chromacomponents Cb and Cr. In addition, it may mean that including the blocksand a syntax element of each block. Each coding tree unit may bepartitioned by using at least one of a quad-tree partitioning method, abinary-tree partitioning method and ternary-tree partitioning method toconfigure a lower unit such as coding unit, prediction unit, transformunit, etc. It may be used as a term for designating a sample block thatbecomes a process unit when encoding/decoding an image as an inputimage. Here, the quad-tree may mean a quarternary-tree.

When the size of the coding block is within a predetermined range, thedivision is possible using only quad-tree partitioning. Here, thepredetermined range may be defined as at least one of a maximum size anda minimum size of a coding block in which the division is possible usingonly quad-tree partitioning. Information indicating a maximum/minimumsize of a coding block in which quad-tree partitioning is allowed may besignaled through a bitstream, and the information may be signaled in atleast one unit of a sequence, a picture parameter, a tile group, or aslice (segment). Alternatively, the maximum/minimum size of the codingblock may be a fixed size predetermined in the coder/decoder. Forexample, when the size of the coding block corresponds to 256×256 to64×64, the division is possible only using quad-tree partitioning.Alternatively, when the size of the coding block is larger than the sizeof the maximum conversion block, the division is possible only usingquad-tree partitioning. Herein, the block to be divided may be at leastone of a coding block and a transform block. In this case, informationindicating the division of the coded block (for example, split_flag) maybe a flag indicating whether or not to perform the quad-treepartitioning. When the size of the coding block falls within apredetermined range, the division is possible only using binary tree orternary tree partitioning. In this case, the above description of thequad-tree partitioning may be applied to binary tree partitioning orternary tree partitioning in the same manner.

Coding Tree Block: may be used as a term for designating any one of a Ycoding tree block, Cb coding tree block, and Cr coding tree block.

Neighbor Block: may mean a block adjacent to a current block. The blockadjacent to the current block may mean a block that comes into contactwith a boundary of the current block, or a block positioned within apredetermined distance from the current block. The neighbor block maymean a block adjacent to a vertex of the current block. Herein, theblock adjacent to the vertex of the current block may mean a blockvertically adjacent to a neighbor block that is horizontally adjacent tothe current block, or a block horizontally adjacent to a neighbor blockthat is vertically adjacent to the current block.

Reconstructed Neighbor block: may mean a neighbor block adjacent to acurrent block and which has been already spatially/temporally encoded ordecoded. Herein, the reconstructed neighbor block may mean areconstructed neighbor unit. A reconstructed spatial neighbor block maybe a block within a current picture and which has been alreadyreconstructed through encoding or decoding or both. A reconstructedtemporal neighbor block is a block at a corresponding position as thecurrent block of the current picture within a reference image, or aneighbor block thereof.

Unit Depth: may mean a partitioned degree of a unit. In a treestructure, the highest node(Root Node) may correspond to the first unitwhich is not partitioned. Also, the highest node may have the leastdepth value. In this case, the highest node may have a depth of level 0.A node having a depth of level 1 may represent a unit generated bypartitioning once the first unit. A node having a depth of level 2 mayrepresent a unit generated by partitioning twice the first unit. A nodehaving a depth of level n may represent a unit generated by partitioningn-times the first unit. A Leaf Node may be the lowest node and a nodewhich cannot be partitioned further. A depth of a Leaf Node may be themaximum level. For example, a predefined value of the maximum level maybe 3. A depth of a root node may be the lowest and a depth of a leafnode may be the deepest. In addition, when a unit is expressed as a treestructure, a level in which a unit is present may mean a unit depth.

Bitstream: may mean a bitstream including encoding image information.

Parameter Set: corresponds to header information among a configurationwithin a bitstream. At least one of a video parameter set, a sequenceparameter set, a picture parameter set, and an adaptation parameter setmay be included in a parameter set. In addition, a parameter set mayinclude a slice header, a tile group header, and tile headerinformation. The term “tile group” means a group of tiles and has thesame meaning as a slice.

An adaptation parameter set may mean a parameter set that can be sharedby being referred to in different pictures, subpictures, slices, tilegroups, tiles, or bricks. In addition, information in an adaptationparameter set may be used by referring to different adaptation parametersets for a subpicture, a slice, a tile group, a tile, or a brick insidea picture.

In addition, regarding the adaptation parameter set, differentadaptation parameter sets may be referred to by using identifiers ofdifferent adaptation parameter sets for a subpicture, a slice, a tilegroup, a tile, or a brick inside a picture.

In addition, regarding the adaptation parameter set, differentadaptation parameter sets may be referred to by using identifiers ofdifferent adaptation parameter sets for a slice, a tile group, a tile,or a brick inside a subpicture.

In addition, regarding the adaptation parameter set, differentadaptation parameter sets may be referred to by using identifiers ofdifferent adaptation parameter sets for a tile or a brick inside aslice.

In addition, regarding the adaptation parameter set, differentadaptation parameter sets may be referred to by using identifiers ofdifferent adaptation parameter sets for a brick inside a tile.

Information on an adaptation parameter set identifier may be included ina parameter set or a header of the subpicture, and an adaptationparameter set corresponding to the adaptation parameter set identifiermay be used for the subpicture.

The information on the adaptation parameter set identifier may beincluded in a parameter set or a header of the tile, and an adaptationparameter set corresponding to the adaptation parameter set identifiermay be used for the tile.

The information on the adaptation parameter set identifier may beincluded in a header of the brick, and an adaptation parameter setcorresponding to the adaptation parameter set identifier may be used forthe brick.

The picture may be partitioned into one or more tile rows and one ormore tile columns.

The subpicture may be partitioned into one or more tile rows and one ormore tile columns within a picture. The subpicture may be a regionhaving the form of a rectangle/square within a picture and may includeone or more CTUs. In addition, at least one or more tiles/bricks/slicesmay be included within one subpicture.

The tile may be a region having the form of a rectangle/square within apicture and may include one or more CTUs. In addition, the tile may bepartitioned into one or more bricks.

The brick may mean one or more CTU rows within a tile. The tile may bepartitioned into one or more bricks, and each brick may have at leastone or more CTU rows. A tile that is not partitioned into two or moremay mean a brick.

The slice may include one or more tiles within a picture and may includeone or more bricks within a tile.

Parsing: may mean determination of a value of a syntax element byperforming entropy decoding, or may mean the entropy decoding itself.

Symbol: may mean at least one of a syntax element, a coding parameter,and a transform coefficient value of an encoding/decoding target unit.In addition, the symbol may mean an entropy encoding target or anentropy decoding result.

Prediction Mode: may be information indicating a mode encoded/decodedwith intra prediction or a mode encoded/decoded with inter prediction.

Prediction Unit: may mean a basic unit when performing prediction suchas inter-prediction, intra-prediction, inter-compensation,intra-compensation, and motion compensation. A single prediction unitmay be partitioned into a plurality of partitions having a smaller size,or may be partitioned into a plurality of lower prediction units. Aplurality of partitions may be a basic unit in performing prediction orcompensation. A partition which is generated by dividing a predictionunit may also be a prediction unit.

Prediction Unit Partition: may mean a form obtained by partitioning aprediction unit.

Reference picture list may refer to a list including one or morereference pictures used for inter prediction or motion compensation.There are several types of usable reference picture lists, including LC(List combined), L0 (List 0), L1 (List 1), L2 (List 2), L3 (List 3).

Inter prediction indicator may refer to a direction of inter prediction(unidirectional prediction, bidirectional prediction, etc.) of a currentblock. Alternatively, it may refer to the number of reference picturesused to generate a prediction block of a current block. Alternatively,it may refer to the number of prediction blocks used at the time ofperforming inter prediction or motion compensation on a current block.

Prediction list utilization flag indicates whether a prediction block isgenerated using at least one reference picture in a specific referencepicture list. An inter prediction indicator can be derived using aprediction list utilization flag, and conversely, a prediction listutilization flag can be derived using an inter prediction indicator. Forexample, when the prediction list utilization flag has a first value ofzero (0), it means that a reference picture in a reference picture listis not used to generate a prediction block. On the other hand, when theprediction list utilization flag has a second value of one (1), it meansthat a reference picture list is used to generate a prediction block.

Reference picture index may refer to an index indicating a specificreference picture in a reference picture list.

Reference picture may mean a reference picture which is referred to by aspecific block for the purposes of inter prediction or motioncompensation of the specific block. Alternatively, the reference picturemay be a picture including a reference block referred to by a currentblock for inter prediction or motion compensation. Hereinafter, theterms “reference picture” and “reference image” have the same meaningand can be interchangeably.

Motion vector may be a two-dimensional vector used for inter predictionor motion compensation. The motion vector may mean an offset between anencoding/decoding target block and a reference block. For example, (mvX,mvY) may represent a motion vector. Here, mvX may represent a horizontalcomponent and mvY may represent a vertical component.

Search range may be a two-dimensional region which is searched toretrieve a motion vector during inter prediction. For example, the sizeof the search range may be M×N. Here, M and N are both integers.

Motion vector candidate may refer to a prediction candidate block or amotion vector of the prediction candidate block when predicting a motionvector. In addition, a motion vector candidate may be included in amotion vector candidate list.

Motion vector candidate list may mean a list composed of one or moremotion vector candidates.

Motion vector candidate index may mean an indicator indicating a motionvector candidate in a motion vector candidate list. Alternatively, itmay be an index of a motion vector predictor.

Motion information may mean information including at least one of theitems including a motion vector, a reference picture index, an interprediction indicator, a prediction list utilization flag, referencepicture list information, a reference picture, a motion vectorcandidate, a motion vector candidate index, a merge candidate, and amerge index.

Merge candidate list may mean a list composed of one or more mergecandidates.

Merge candidate may mean a spatial merge candidate, a temporal mergecandidate, a combined merge candidate, a combined bi-predictive mergecandidate, or a zero merge candidate. The merge candidate may includemotion information such as an inter prediction indicator, a referencepicture index for each list, a motion vector, a prediction listutilization flag, and an inter prediction indicator.

Merge index may mean an indicator indicating a merge candidate in amerge candidate list. Alternatively, the merge index may indicate ablock from which a merge candidate has been derived, among reconstructedblocks spatially/temporally adjacent to a current block. Alternatively,the merge index may indicate at least one piece of motion information ofa merge candidate.

Transform Unit: may mean a basic unit when performing encoding/decodingsuch as transform, inverse-transform, quantization, dequantization,transform coefficient encoding/decoding of a residual signal. A singletransform unit may be partitioned into a plurality of lower-leveltransform units having a smaller size. Here,transformation/inverse-transformation may comprise at least one amongthe first transformation/the first inverse-transformation and the secondtransformation/the second inverse-transformation.

Scaling: may mean a process of multiplying a quantized level by afactor. A transform coefficient may be generated by scaling a quantizedlevel. The scaling also may be referred to as dequantization.

Quantization Parameter: may mean a value used when generating aquantized level using a transform coefficient during quantization. Thequantization parameter also may mean a value used when generating atransform coefficient by scaling a quantized level duringdequantization. The quantization parameter may be a value mapped on aquantization step size.

Delta Quantization Parameter: may mean a difference value between apredicted quantization parameter and a quantization parameter of anencoding/decoding target unit.

Scan: may mean a method of sequencing coefficients within a unit, ablock or a matrix. For example, changing a two-dimensional matrix ofcoefficients into a one-dimensional matrix may be referred to asscanning, and changing a one-dimensional matrix of coefficients into atwo-dimensional matrix may be referred to as scanning or inversescanning.

Transform Coefficient: may mean a coefficient value generated aftertransform is performed in an encoder. It may mean a coefficient valuegenerated after at least one of entropy decoding and dequantization isperformed in a decoder. A quantized level obtained by quantizing atransform coefficient or a residual signal, or a quantized transformcoefficient level also may fall within the meaning of the transformcoefficient.

Quantized Level: may mean a value generated by quantizing a transformcoefficient or a residual signal in an encoder. Alternatively, thequantized level may mean a value that is a dequantization target toundergo dequantization in a decoder. Similarly, a quantized transformcoefficient level that is a result of transform and quantization alsomay fall within the meaning of the quantized level.

Non-zero Transform Coefficient: may mean a transform coefficient havinga value other than zero, or a transform coefficient level or a quantizedlevel having a value other than zero.

Quantization Matrix: may mean a matrix used in a quantization process ora dequantization process performed to improve subjective or objectiveimage quality. The quantization matrix also may be referred to as ascaling list.

Quantization Matrix Coefficient: may mean each element within aquantization matrix. The quantization matrix coefficient also may bereferred to as a matrix coefficient.

Default Matrix: may mean a predetermined quantization matrixpreliminarily defined in an encoder or a decoder.

Non-default Matrix: may mean a quantization matrix that is notpreliminarily defined in an encoder or a decoder but is signaled by auser.

Statistic Value: a statistic value for at least one among a variable, acoding parameter, a constant value, etc. which have a computablespecific value may be one or more among an average value, a sum value, aweighted average value, a weighted sum value, the minimum value, themaximum value, the most frequent value, a median value, an interpolatedvalue of the corresponding specific values.

FIG. 1 is a block diagram showing a configuration of an encodingapparatus according to an embodiment to which the present invention isapplied.

An encoding apparatus 100 may be an encoder, a video encoding apparatus,or an image encoding apparatus. A video may include at least one image.The encoding apparatus 100 may sequentially encode at least one image.

Referring to FIG. 1, the encoding apparatus 100 may include a motionprediction unit 111, a motion compensation unit 112, an intra-predictionunit 120, a switch 115, a subtractor 125, a transform unit 130, aquantization unit 140, an entropy encoding unit 150, a dequantizationunit 160, an inverse-transform unit 170, an adder 175, a filter unit180, and a reference picture buffer 190.

The encoding apparatus 100 may perform encoding of an input image byusing an intra mode or an inter mode or both. In addition, encodingapparatus 100 may generate a bitstream including encoded informationthrough encoding the input image, and output the generated bitstream.The generated bitstream may be stored in a computer readable recordingmedium, or may be streamed through a wired/wireless transmission medium.When an intra mode is used as a prediction mode, the switch 115 may beswitched to an intra. Alternatively, when an inter mode is used as aprediction mode, the switch 115 may be switched to an inter mode.Herein, the intra mode may mean an intra-prediction mode, and the intermode may mean an inter-prediction mode. The encoding apparatus 100 maygenerate a prediction block for an input block of the input image. Inaddition, the encoding apparatus 100 may encode a residual block using aresidual of the input block and the prediction block after theprediction block being generated. The input image may be called as acurrent image that is a current encoding target. The input block may becalled as a current block that is current encoding target, or as anencoding target block.

When a prediction mode is an intra mode, the intra-prediction unit 120may use a sample of a block that has been already encoded/decoded and isadjacent to a current block as a reference sample. The intra-predictionunit 120 may perform spatial prediction for the current block by using areference sample, or generate prediction samples of an input block byperforming spatial prediction. Herein, the intra prediction may meanintra-prediction,

When a prediction mode is an inter mode, the motion prediction unit 111may retrieve a region that best matches with an input block from areference image when performing motion prediction, and deduce a motionvector by using the retrieved region. In this case, a search region maybe used as the region. The reference image may be stored in thereference picture buffer 190. Here, when encoding/decoding for thereference image is performed, it may be stored in the reference picturebuffer 190.

The motion compensation unit 112 may generate a prediction block byperforming motion compensation for the current block using a motionvector. Herein, inter-prediction may mean inter-prediction or motioncompensation.

When the value of the motion vector is not an integer, the motionprediction unit 111 and the motion compensation unit 112 may generatethe prediction block by applying an interpolation filter to a partialregion of the reference picture. In order to perform inter-pictureprediction or motion compensation on a coding unit, it may be determinedthat which mode among a skip mode, a merge mode, an advanced motionvector prediction (AMVP) mode, and a current picture referring mode isused for motion prediction and motion compensation of a prediction unitincluded in the corresponding coding unit. Then, inter-pictureprediction or motion compensation may be differently performed dependingon the determined mode.

The subtractor 125 may generate a residual block by using a differenceof an input block and a prediction block. The residual block may becalled as a residual signal. The residual signal may mean a differencebetween an original signal and a prediction signal. In addition, theresidual signal may be a signal generated by transforming or quantizing,or transforming and quantizing a difference between the original signaland the prediction signal. The residual block may be a residual signalof a block unit.

The transform unit 130 may generate a transform coefficient byperforming transform of a residual block, and output the generatedtransform coefficient. Herein, the transform coefficient may be acoefficient value generated by performing transform of the residualblock. When a transform skip mode is applied, the transform unit 130 mayskip transform of the residual block.

A quantized level may be generated by applying quantization to thetransform coefficient or to the residual signal. Hereinafter, thequantized level may be also called as a transform coefficient inembodiments.

The quantization unit 140 may generate a quantized level by quantizingthe transform coefficient or the residual signal according to aparameter, and output the generated quantized level. Herein, thequantization unit 140 may quantize the transform coefficient by using aquantization matrix.

The entropy encoding unit 150 may generate a bitstream by performingentropy encoding according to a probability distribution on valuescalculated by the quantization unit 140 or on coding parameter valuescalculated when performing encoding, and output the generated bitstream.The entropy encoding unit 150 may perform entropy encoding of sampleinformation of an image and information for decoding an image. Forexample, the information for decoding the image may include a syntaxelement.

When entropy encoding is applied, symbols are represented so that asmaller number of bits are assigned to a symbol having a high chance ofbeing generated and a larger number of bits are assigned to a symbolhaving a low chance of being generated, and thus, the size of bit streamfor symbols to be encoded may be decreased. The entropy encoding unit150 may use an encoding method for entropy encoding such as exponentialGolomb, context-adaptive variable length coding (CAVLC),context-adaptive binary arithmetic coding (CABAC), etc. For example, theentropy encoding unit 150 may perform entropy encoding by using avariable length coding/code (VLC) table. In addition, the entropyencoding unit 150 may deduce a binarization method of a target symboland a probability model of a target symbol/bin, and perform arithmeticcoding by using the deduced binarization method, and a context model.

In order to encode a transform coefficient level (quantized level), theentropy encoding unit 150 may change a two-dimensional block formcoefficient into a one-dimensional vector form by using a transformcoefficient scanning method.

A coding parameter may include information (flag, index, etc.) such assyntax element that is encoded in an encoder and signaled to a decoder,and information derived when performing encoding or decoding. The codingparameter may mean information required when encoding or decoding animage. For example, at least one value or a combination form of aunit/block size, a unit/block depth, unit/block partition information,unit/block shape, unit/block partition structure, whether to partitionof a quad-tree form, whether to partition of a binary-tree form, apartition direction of a binary-tree form (horizontal direction orvertical direction), a partition form of a binary-tree form (symmetricpartition or asymmetric partition), whether or not a current coding unitis partitioned by ternary tree partitioning, direction (horizontal orvertical direction) of the ternary tree partitioning, type (symmetric orasymmetric type) of the ternary tree partitioning, whether a currentcoding unit is partitioned by multi-type tree partitioning, direction(horizontal or vertical direction) of the multi-type three partitioning,type (symmetric or asymmetric type) of the multi-type tree partitioning,and a tree (binary tree or ternary tree) structure of the multi-typetree partitioning, a prediction mode(intra prediction or interprediction), a luma intra-prediction mode/direction, a chromaintra-prediction mode/direction, intra partition information, interpartition information, a coding block partition flag, a prediction blockpartition flag, a transform block partition flag, a reference samplefiltering method, a reference sample filter tab, a reference samplefilter coefficient, a prediction block filtering method, a predictionblock filter tap, a prediction block filter coefficient, a predictionblock boundary filtering method, a prediction block boundary filter tab,a prediction block boundary filter coefficient, an intra-predictionmode, an inter-prediction mode, motion information, a motion vector, amotion vector difference, a reference picture index, a inter-predictionangle, an inter-prediction indicator, a prediction list utilizationflag, a reference picture list, a reference picture, a motion vectorpredictor index, a motion vector predictor candidate, a motion vectorcandidate list, whether to use a merge mode, a merge index, a mergecandidate, a merge candidate list, whether to use a skip mode, aninterpolation filter type, an interpolation filter tab, an interpolationfilter coefficient, a motion vector size, a presentation accuracy of amotion vector, a transform type, a transform size, information ofwhether or not a primary (first) transform is used, information ofwhether or not a secondary transform is used, a primary transform index,a secondary transform index, information of whether or not a residualsignal is present, a coded block pattern, a coded block flag (CBF), aquantization parameter, a quantization parameter residue, a quantizationmatrix, whether to apply an intra loop filter, an intra loop filtercoefficient, an intra loop filter tab, an intra loop filter shape/form,whether to apply a deblocking filter, a deblocking filter coefficient, adeblocking filter tab, a deblocking filter strength, a deblocking filtershape/form, whether to apply an adaptive sample offset, an adaptivesample offset value, an adaptive sample offset category, an adaptivesample offset type, whether to apply an adaptive loop filter, anadaptive loop filter coefficient, an adaptive loop filter tab, anadaptive loop filter shape/form, a binarization/inverse-binarizationmethod, a context model determining method, a context model updatingmethod, whether to perform a regular mode, whether to perform a bypassmode, a context bin, a bypass bin, a significant coefficient flag, alast significant coefficient flag, a coded flag for a unit of acoefficient group, a position of the last significant coefficient, aflag for whether a value of a coefficient is larger than 1, a flag forwhether a value of a coefficient is larger than 2, a flag for whether avalue of a coefficient is larger than 3, information on a remainingcoefficient value, a sign information, a reconstructed luma sample, areconstructed chroma sample, a residual luma sample, a residual chromasample, a luma transform coefficient, a chroma transform coefficient, aquantized luma level, a quantized chroma level, a transform coefficientlevel scanning method, a size of a motion vector search area at adecoder side, a shape of a motion vector search area at a decoder side,a number of time of a motion vector search at a decoder side,information on a CTU size, information on a minimum block size,information on a maximum block size, information on a maximum blockdepth, information on a minimum block depth, an imagedisplaying/outputting sequence, slice identification information, aslice type, slice partition information, tile identificationinformation, a tile type, tile partition information, tile groupidentification information, a tile group type, tile group partitioninformation, a picture type, a bit depth of an input sample, a bit depthof a reconstruction sample, a bit depth of a residual sample, a bitdepth of a transform coefficient, a bit depth of a quantized level, andinformation on a luma signal or information on a chroma signal may beincluded in the coding parameter.

Herein, signaling the flag or index may mean that a corresponding flagor index is entropy encoded and included in a bitstream by an encoder,and may mean that the corresponding flag or index is entropy decodedfrom a bitstream by a decoder.

When the encoding apparatus 100 performs encoding throughinter-prediction, an encoded current image may be used as a referenceimage for another image that is processed afterwards. Accordingly, theencoding apparatus 100 may reconstruct or decode the encoded currentimage, or store the reconstructed or decoded image as a reference imagein reference picture buffer 190.

A quantized level may be dequantized in the dequantization unit 160, ormay be inverse-transformed in the inverse-transform unit 170. Adequantized or inverse-transformed coefficient or both may be added witha prediction block by the adder 175. By adding the dequantized orinverse-transformed coefficient or both with the prediction block, areconstructed block may be generated. Herein, the dequantized orinverse-transformed coefficient or both may mean a coefficient on whichat least one of dequantization and inverse-transform is performed, andmay mean a reconstructed residual block.

A reconstructed block may pass through the filter unit 180. The filterunit 180 may apply at least one of a deblocking filter, a sampleadaptive offset (SAO), and an adaptive loop filter (ALF) to areconstructed sample, a reconstructed block or a reconstructed image.The filter unit 180 may be called as an in-loop filter.

The deblocking filter may remove block distortion generated inboundaries between blocks. In order to determine whether or not to applya deblocking filter, whether or not to apply a deblocking filter to acurrent block may be determined based samples included in several rowsor columns which are included in the block. When a deblocking filter isapplied to a block, another filter may be applied according to arequired deblocking filtering strength.

In order to compensate an encoding error, a proper offset value may beadded to a sample value by using a sample adaptive offset. The sampleadaptive offset may correct an offset of a deblocked image from anoriginal image by a sample unit. A method of partitioning samples of animage into a predetermined number of regions, determining a region towhich an offset is applied, and applying the offset to the determinedregion, or a method of applying an offset in consideration of edgeinformation on each sample may be used.

The adaptive loop filter may perform filtering based on a comparisonresult of the filtered reconstructed image and the original image.Samples included in an image may be partitioned into predeterminedgroups, a filter to be applied to each group may be determined, anddifferential filtering may be performed for each group. Information ofwhether or not to apply the ALF may be signaled by coding units (CUs),and a form and coefficient of the ALF to be applied to each block mayvary.

The reconstructed block or the reconstructed image having passed throughthe filter unit 180 may be stored in the reference picture buffer 190. Areconstructed block processed by the filter unit 180 may be a part of areference image. That is, a reference image is a reconstructed imagecomposed of reconstructed blocks processed by the filter unit 180. Thestored reference image may be used later in inter prediction or motioncompensation.

FIG. 2 is a block diagram showing a configuration of a decodingapparatus according to an embodiment and to which the present inventionis applied.

A decoding apparatus 200 may a decoder, a video decoding apparatus, oran image decoding apparatus.

Referring to FIG. 2, the decoding apparatus 200 may include an entropydecoding unit 210, a dequantization unit 220, an inverse-transform unit230, an intra-prediction unit 240, a motion compensation unit 250, anadder 225, a filter unit 260, and a reference picture buffer 270.

The decoding apparatus 200 may receive a bitstream output from theencoding apparatus 100. The decoding apparatus 200 may receive abitstream stored in a computer readable recording medium, or may receivea bitstream that is streamed through a wired/wireless transmissionmedium. The decoding apparatus 200 may decode the bitstream by using anintra mode or an inter mode. In addition, the decoding apparatus 200 maygenerate a reconstructed image generated through decoding or a decodedimage, and output the reconstructed image or decoded image.

When a prediction mode used when decoding is an intra mode, a switch maybe switched to an intra. Alternatively, when a prediction mode used whendecoding is an inter mode, a switch may be switched to an inter mode.

The decoding apparatus 200 may obtain a reconstructed residual block bydecoding the input bitstream, and generate a prediction block. When thereconstructed residual block and the prediction block are obtained, thedecoding apparatus 200 may generate a reconstructed block that becomes adecoding target by adding the reconstructed residual block with theprediction block. The decoding target block may be called a currentblock.

The entropy decoding unit 210 may generate symbols by entropy decodingthe bitstream according to a probability distribution. The generatedsymbols may include a symbol of a quantized level form. Herein, anentropy decoding method may be an inverse-process of the entropyencoding method described above.

In order to decode a transform coefficient level (quantized level), theentropy decoding unit 210 may change a one-directional vector formcoefficient into a two-dimensional block form by using a transformcoefficient scanning method.

A quantized level may be dequantized in the dequantization unit 220, orinverse-transformed in the inverse-transform unit 230. The quantizedlevel may be a result of dequantizing or inverse-transforming or both,and may be generated as a reconstructed residual block. Herein, thedequantization unit 220 may apply a quantization matrix to the quantizedlevel.

When an intra mode is used, the intra-prediction unit 240 may generate aprediction block by performing, for the current block, spatialprediction that uses a sample value of a block adjacent to a decodingtarget block and which has been already decoded.

When an inter mode is used, the motion compensation unit 250 maygenerate a prediction block by performing, for the current block, motioncompensation that uses a motion vector and a reference image stored inthe reference picture buffer 270.

The adder 225 may generate a reconstructed block by adding thereconstructed residual block with the prediction block. The filter unit260 may apply at least one of a deblocking filter, a sample adaptiveoffset, and an adaptive loop filter to the reconstructed block orreconstructed image. The filter unit 260 may output the reconstructedimage. The reconstructed block or reconstructed image may be stored inthe reference picture buffer 270 and used when performinginter-prediction. A reconstructed block processed by the filter unit 260may be a part of a reference image. That is, a reference image is areconstructed image composed of reconstructed blocks processed by thefilter unit 260. The stored reference image may be used later in interprediction or motion compensation.

FIG. 3 is a view schematically showing a partition structure of an imagewhen encoding and decoding the image. FIG. 3 schematically shows anexample of partitioning a single unit into a plurality of lower units.

In order to efficiently partition an image, when encoding and decoding,a coding unit (CU) may be used. The coding unit may be used as a basicunit when encoding/decoding the image. In addition, the coding unit maybe used as a unit for distinguishing an intra prediction mode and aninter prediction mode when encoding/decoding the image. The coding unitmay be a basic unit used for prediction, transform, quantization,inverse-transform, dequantization, or an encoding/decoding process of atransform coefficient.

Referring to FIG. 3, an image 300 is sequentially partitioned in alargest coding unit (LCU), and a LCU unit is determined as a partitionstructure. Herein, the LCU may be used in the same meaning as a codingtree unit (CTU). A unit partitioning may mean partitioning a blockassociated with to the unit. In block partition information, informationof a unit depth may be included. Depth information may represent anumber of times or a degree or both in which a unit is partitioned. Asingle unit may be partitioned into a plurality of lower level unitshierarchically associated with depth information based on a treestructure. In other words, a unit and a lower level unit generated bypartitioning the unit may correspond to a node and a child node of thenode, respectively. Each of partitioned lower unit may have depthinformation. Depth information may be information representing a size ofa CU, and may be stored in each CU. Unit depth represents times and/ordegrees related to partitioning a unit. Therefore, partitioninginformation of a lower-level unit may comprise information on a size ofthe lower-level unit.

A partition structure may mean a distribution of a coding unit (CU)within an LCU 310. Such a distribution may be determined according towhether or not to partition a single CU into a plurality (positiveinteger equal to or greater than 2 including 2, 4, 8, 16, etc.) of CUs.A horizontal size and a vertical size of the CU generated bypartitioning may respectively be half of a horizontal size and avertical size of the CU before partitioning, or may respectively havesizes smaller than a horizontal size and a vertical size beforepartitioning according to a number of times of partitioning. The CU maybe recursively partitioned into a plurality of CUs. By the recursivepartitioning, at least one among a height and a width of a CU afterpartitioning may decrease comparing with at least one among a height anda width of a CU before partitioning. Partitioning of the CU may berecursively performed until to a predefined depth or predefined size.For example, a depth of an LCU may be 0, and a depth of a smallestcoding unit (SCU) may be a predefined maximum depth. Herein, the LCU maybe a coding unit having a maximum coding unit size, and the SCU may be acoding unit having a minimum coding unit size as described above.Partitioning is started from the LCU 310, a CU depth increases by 1 as ahorizontal size or a vertical size or both of the CU decreases bypartitioning. For example, for each depth, a CU which is not partitionedmay have a size of 2N×2N. Also, in case of a CU which is partitioned, aCU with a size of 2N×2N may be partitioned into four CUs with a size ofN×N. A size of N may decrease to half as a depth increase by 1.

In addition, information whether or not the CU is partitioned may berepresented by using partition information of the CU. The partitioninformation may be 1-bit information. All CUs, except for a SCU, mayinclude partition information. For example, when a value of partitioninformation is a first value, the CU may not be partitioned, when avalue of partition information is a second value, the CU may bepartitioned

Referring to FIG. 3, an LCU having a depth 0 may be a 64×64 block. 0 maybe a minimum depth. A SCU having a depth 3 may be an 8×8 block. 3 may bea maximum depth. A CU of a 32×32 block and a 16×16 block may berespectively represented as a depth 1 and a depth 2.

For example, when a single coding unit is partitioned into four codingunits, a horizontal size and a vertical size of the four partitionedcoding units may be a half size of a horizontal and vertical size of theCU before being partitioned. In one embodiment, when a coding unithaving a 32×32 size is partitioned into four coding units, each of thefour partitioned coding units may have a 16×16 size. When a singlecoding unit is partitioned into four coding units, it may be called thatthe coding unit may be partitioned into a quad-tree form.

For example, when one coding unit is partitioned into two sub-codingunits, the horizontal or vertical size (width or height) of each of thetwo sub-coding units may be half the horizontal or vertical size of theoriginal coding unit. For example, when a coding unit having a size of32×32 is vertically partitioned into two sub-coding units, each of thetwo sub-coding units may have a size of 16×32. For example, when acoding unit having a size of 8×32 is horizontally partitioned into twosub-coding units, each of the two sub-coding units may have a size of8×16. When one coding unit is partitioned into two sub-coding units, itcan be said that the coding unit is binary-partitioned or is partitionedby a binary tree partition structure.

For example, when one coding unit is partitioned into three sub-codingunits, the horizontal or vertical size of the coding unit can bepartitioned with a ratio of 1:2:1, thereby producing three sub-codingunits whose horizontal or vertical sizes are in a ratio of 1:2:1. Forexample, when a coding unit having a size of 16×32 is horizontallypartitioned into three sub-coding units, the three sub-coding units mayhave sizes of 16×8, 16×16, and 16×8 respectively, in the order from theuppermost to the lowermost sub-coding unit. For example, when a codingunit having a size of 32×32 is vertically split into three sub-codingunits, the three sub-coding units may have sizes of 8×32, 16×32, and8×32, respectively in the order from the left to the right sub-codingunit. When one coding unit is partitioned into three sub-coding units,it can be said that the coding unit is ternary-partitioned orpartitioned by a ternary tree partition structure.

In FIG. 3, a coding tree unit (CTU) 320 is an example of a CTU to whicha quad tree partition structure, a binary tree partition structure, anda ternary tree partition structure are all applied.

As described above, in order to partition the CTU, at least one of aquad tree partition structure, a binary tree partition structure, and aternary tree partition structure may be applied. Various tree partitionstructures may be sequentially applied to the CTU, according to apredetermined priority order. For example, the quad tree partitionstructure may be preferentially applied to the CTU. A coding unit thatcannot be partitioned any longer using a quad tree partition structuremay correspond to a leaf node of a quad tree. A coding unitcorresponding to a leaf node of a quad tree may serve as a root node ofa binary and/or ternary tree partition structure. That is, a coding unitcorresponding to a leaf node of a quad tree may be further partitionedby a binary tree partition structure or a ternary tree partitionstructure, or may not be further partitioned. Therefore, by preventing acoding unit that results from binary tree partitioning or ternary treepartitioning of a coding unit corresponding to a leaf node of a quadtree from undergoing further quad tree partitioning, block partitioningand/or signaling of partition information can be effectively performed.

The fact that a coding unit corresponding to a node of a quad tree ispartitioned may be signaled using quad partition information. The quadpartition information having a first value (e.g., “1”) may indicate thata current coding unit is partitioned by the quad tree partitionstructure. The quad partition information having a second value (e.g.,“0”) may indicate that a current coding unit is not partitioned by thequad tree partition structure. The quad partition information may be aflag having a predetermined length (e.g., one bit).

There may not be a priority between the binary tree partitioning and theternary tree partitioning. That is, a coding unit corresponding to aleaf node of a quad tree may further undergo arbitrary partitioningamong the binary tree partitioning and the ternary tree partitioning. Inaddition, a coding unit generated through the binary tree partitioningor the ternary tree partitioning may undergo a further binary treepartitioning or a further ternary tree partitioning, or may not befurther partitioned.

A tree structure in which there is no priority among the binary treepartitioning and the ternary tree partitioning is referred to as amulti-type tree structure. A coding unit corresponding to a leaf node ofa quad tree may serve as a root node of a multi-type tree. Whether topartition a coding unit which corresponds to a node of a multi-type treemay be signaled using at least one of multi-type tree partitionindication information, partition direction information, and partitiontree information. For partitioning of a coding unit corresponding to anode of a multi-type tree, the multi-type tree partition indicationinformation, the partition direction, and the partition tree informationmay be sequentially signaled.

The multi-type tree partition indication information having a firstvalue (e.g., “1”) may indicate that a current coding unit is to undergoa multi-type tree partitioning. The multi-type tree partition indicationinformation having a second value (e.g., “0”) may indicate that acurrent coding unit is not to undergo a multi-type tree partitioning.

When a coding unit corresponding to a node of a multi-type tree isfurther partitioned by a multi-type tree partition structure, the codingunit may include partition direction information. The partitiondirection information may indicate in which direction a current codingunit is to be partitioned for the multi-type tree partitioning. Thepartition direction information having a first value (e.g., “1”) mayindicate that a current coding unit is to be vertically partitioned. Thepartition direction information having a second value (e.g., “0”) mayindicate that a current coding unit is to be horizontally partitioned.

When a coding unit corresponding to a node of a multi-type tree isfurther partitioned by a multi-type tree partition structure, thecurrent coding unit may include partition tree information. Thepartition tree information may indicate a tree partition structure whichis to be used for partitioning of a node of a multi-type tree. Thepartition tree information having a first value (e.g., “1”) may indicatethat a current coding unit is to be partitioned by a binary treepartition structure. The partition tree information having a secondvalue (e.g., “0”) may indicate that a current coding unit is to bepartitioned by a ternary tree partition structure.

The partition indication information, the partition tree information,and the partition direction information may each be a flag having apredetermined length (e.g., one bit).

At least any one of the quadtree partition indication information, themulti-type tree partition indication information, the partitiondirection information, and the partition tree information may be entropyencoded/decoded. For the entropy-encoding/decoding of those types ofinformation, information on a neighboring coding unit adjacent to thecurrent coding unit may be used. For example, there is a highprobability that the partition type (the partitioned or non-partitioned,the partition tree, and/or the partition direction) of a leftneighboring coding unit and/or an upper neighboring coding unit of acurrent coding unit is similar to that of the current coding unit.Therefore, context information for entropy encoding/decoding of theinformation on the current coding unit may be derived from theinformation on the neighboring coding units. The information on theneighboring coding units may include at least any one of quad partitioninformation, multi-type tree partition indication information, partitiondirection information, and partition tree information.

As another example, among binary tree partitioning and ternary treepartitioning, binary tree partitioning may be preferentially performed.That is, a current coding unit may primarily undergo binary treepartitioning, and then a coding unit corresponding to a leaf node of abinary tree may be set as a root node for ternary tree partitioning. Inthis case, neither quad tree partitioning nor binary tree partitioningmay not be performed on the coding unit corresponding to a node of aternary tree.

A coding unit that cannot be partitioned by a quad tree partitionstructure, a binary tree partition structure, and/or a ternary treepartition structure becomes a basic unit for coding, prediction and/ortransformation. That is, the coding unit cannot be further partitionedfor prediction and/or transformation. Therefore, the partition structureinformation and the partition information used for partitioning a codingunit into prediction units and/or transformation units may not bepresent in a bit stream.

However, when the size of a coding unit (i.e., a basic unit forpartitioning) is larger than the size of a maximum transformation block,the coding unit may be recursively partitioned until the size of thecoding unit is reduced to be equal to or smaller than the size of themaximum transformation block. For example, when the size of a codingunit is 64×64 and when the size of a maximum transformation block is32×32, the coding unit may be partitioned into four 32×32 blocks fortransformation. For example, when the size of a coding unit is 32×64 andthe size of a maximum transformation block is 32×32, the coding unit maybe partitioned into two 32×32 blocks for the transformation. In thiscase, the partitioning of the coding unit for transformation is notsignaled separately, and may be determined through comparison betweenthe horizontal or vertical size of the coding unit and the horizontal orvertical size of the maximum transformation block. For example, when thehorizontal size (width) of the coding unit is larger than the horizontalsize (width) of the maximum transformation block, the coding unit may bevertically bisected. For example, when the vertical size (height) of thecoding unit is larger than the vertical size (height) of the maximumtransformation block, the coding unit may be horizontally bisected.

Information of the maximum and/or minimum size of the coding unit andinformation of the maximum and/or minimum size of the transformationblock may be signaled or determined at an upper level of the codingunit. The upper level may be, for example, a sequence level, a picturelevel, a slice level, a tile group level, a tile level, or the like. Forexample, the minimum size of the coding unit may be determined to be4×4. For example, the maximum size of the transformation block may bedetermined to be 64×64. For example, the minimum size of thetransformation block may be determined to be 4×4.

Information of the minimum size (quad tree minimum size) of a codingunit corresponding to a leaf node of a quad tree and/or information ofthe maximum depth (the maximum tree depth of a multi-type tree) from aroot node to a leaf node of the multi-type tree may be signaled ordetermined at an upper level of the coding unit. For example, the upperlevel may be a sequence level, a picture level, a slice level, a tilegroup level, a tile level, or the like. Information of the minimum sizeof a quad tree and/or information of the maximum depth of a multi-typetree may be signaled or determined for each of an intra-picture sliceand an inter-picture slice.

Difference information between the size of a CTU and the maximum size ofa transformation block may be signaled or determined at an upper levelof the coding unit. For example, the upper level may be a sequencelevel, a picture level, a slice level, a tile group level, a tile level,or the like. Information of the maximum size of the coding unitscorresponding to the respective nodes of a binary tree (hereinafter,referred to as a maximum size of a binary tree) may be determined basedon the size of the coding tree unit and the difference information. Themaximum size of the coding units corresponding to the respective nodesof a ternary tree (hereinafter, referred to as a maximum size of aternary tree) may vary depending on the type of slice. For example, foran intra-picture slice, the maximum size of a ternary tree may be 32×32.For example, for an inter-picture slice, the maximum size of a ternarytree may be 128×128. For example, the minimum size of the coding unitscorresponding to the respective nodes of a binary tree (hereinafter,referred to as a minimum size of a binary tree) and/or the minimum sizeof the coding units corresponding to the respective nodes of a ternarytree (hereinafter, referred to as a minimum size of a ternary tree) maybe set as the minimum size of a coding block.

As another example, the maximum size of a binary tree and/or the maximumsize of a ternary tree may be signaled or determined at the slice level.Alternatively, the minimum size of the binary tree and/or the minimumsize of the ternary tree may be signaled or determined at the slicelevel.

Depending on size and depth information of the above-described variousblocks, quad partition information, multi-type tree partition indicationinformation, partition tree information and/or partition directioninformation may be included or may not be included in a bit stream.

For example, when the size of the coding unit is not larger than theminimum size of a quad tree, the coding unit does not contain quadpartition information. The quad partition information may be deduced asa second value.

For example, when the sizes (horizontal and vertical sizes) of a codingunit corresponding to a node of a multi-type tree are larger than themaximum sizes (horizontal and vertical sizes) of a binary tree and/orthe maximum sizes (horizontal and vertical sizes) of a ternary tree, thecoding unit may not be binary-partitioned or ternary-partitioned.Accordingly, the multi-type tree partition indication information maynot be signaled but may be deduced as a second value.

Alternatively, when the sizes (horizontal and vertical sizes) of acoding unit corresponding to a node of a multi-type tree are the same asthe maximum sizes (horizontal and vertical sizes) of a binary treeand/or are two times as large as the maximum sizes (horizontal andvertical sizes) of a ternary tree, the coding unit may not be furtherbinary-partitioned or ternary-partitioned. Accordingly, the multi-typetree partition indication information may not be signaled but be derivedfrom a second value. This is because when a coding unit is partitionedby a binary tree partition structure and/or a ternary tree partitionstructure, a coding unit smaller than the minimum size of a binary treeand/or the minimum size of a ternary tree is generated.

Alternatively, the binary tree partitioning or the ternary treepartitioning may be limited on the basis of the size of a virtualpipeline data unit (hereinafter, a pipeline buffer size). For example,when the coding unit is divided into sub-coding units which do not fitthe pipeline buffer size by the binary tree partitioning or the ternarytree partitioning, the corresponding binary tree partitioning or ternarytree partitioning may be limited. The pipeline buffer size may be thesize of the maximum transform block (e.g., 64×64). For example, when thepipeline buffer size is 64×64, the division below may be limited.

-   -   N×M (N and/or M is 128) Ternary tree partitioning for coding        units    -   128×N (N<=64) Binary tree partitioning in horizontal direction        for coding units    -   N×128 (N<=64) Binary tree partitioning in vertical direction for        coding units

Alternatively, when the depth of a coding unit corresponding to a nodeof a multi-type tree is equal to the maximum depth of the multi-typetree, the coding unit may not be further binary-partitioned and/orternary-partitioned. Accordingly, the multi-type tree partitionindication information may not be signaled but may be deduced as asecond value.

Alternatively, only when at least one of vertical direction binary treepartitioning, horizontal direction binary tree partitioning, verticaldirection ternary tree partitioning, and horizontal direction ternarytree partitioning is possible for a coding unit corresponding to a nodeof a multi-type tree, the multi-type tree partition indicationinformation may be signaled. Otherwise, the coding unit may not bebinary-partitioned and/or ternary-partitioned. Accordingly, themulti-type tree partition indication information may not be signaled butmay be deduced as a second value.

Alternatively, only when both of the vertical direction binary treepartitioning and the horizontal direction binary tree partitioning orboth of the vertical direction ternary tree partitioning and thehorizontal direction ternary tree partitioning are possible for a codingunit corresponding to a node of a multi-type tree, the partitiondirection information may be signaled. Otherwise, the partitiondirection information may not be signaled but may be derived from avalue indicating possible partitioning directions.

Alternatively, only when both of the vertical direction binary treepartitioning and the vertical direction ternary tree partitioning orboth of the horizontal direction binary tree partitioning and thehorizontal direction ternary tree partitioning are possible for a codingtree corresponding to a node of a multi-type tree, the partition treeinformation may be signaled. Otherwise, the partition tree informationmay not be signaled but be deduced as a value indicating a possiblepartitioning tree structure.

FIG. 4 is a view showing an intra-prediction process.

Arrows from center to outside in FIG. 4 may represent predictiondirections of intra prediction modes.

Intra encoding and/or decoding may be performed by using a referencesample of a neighbor block of the current block. A neighbor block may bea reconstructed neighbor block. For example, intra encoding and/ordecoding may be performed by using a coding parameter or a value of areference sample included in a reconstructed neighbor block.

A prediction block may mean a block generated by performing intraprediction. A prediction block may correspond to at least one among CU,PU and TU. A unit of a prediction block may have a size of one among CU,PU and TU. A prediction block may be a square block having a size of2>2, 4>4, 16×16, 32×32 or 64×64 etc. or may be a rectangular blockhaving a size of 2×8, 4×8, 2×16, 4×16 and 8×16 etc.

Intra prediction may be performed according to intra prediction mode forthe current block. The number of intra prediction modes which thecurrent block may have may be a fixed value and may be a valuedetermined differently according to an attribute of a prediction block.For example, an attribute of a prediction block may comprise a size of aprediction block and a shape of a prediction block, etc.

The number of intra-prediction modes may be fixed to N regardless of ablock size. Or, the number of intra prediction modes may be 3, 5, 9, 17,34, 35, 36, 65, or 67 etc. Alternatively, the number of intra-predictionmodes may vary according to a block size or a color component type orboth. For example, the number of intra prediction modes may varyaccording to whether the color component is a luma signal or a chromasignal. For example, as a block size becomes large, a number ofintra-prediction modes may increase. Alternatively, a number ofintra-prediction modes of a luma component block may be larger than anumber of intra-prediction modes of a chroma component block.

An intra-prediction mode may be a non-angular mode or an angular mode.The non-angular mode may be a DC mode or a planar mode, and the angularmode may be a prediction mode having a specific direction or angle. Theintra-prediction mode may be expressed by at least one of a mode number,a mode value, a mode numeral, a mode angle, and mode direction. A numberof intra-prediction modes may be M, which is larger than 1, includingthe non-angular and the angular mode. In order to intra-predict acurrent block, a step of determining whether or not samples included ina reconstructed neighbor block may be used as reference samples of thecurrent block may be performed. When a sample that is not usable as areference sample of the current block is present, a value obtained byduplicating or performing interpolation on at least one sample valueamong samples included in the reconstructed neighbor block or both maybe used to replace with a non-usable sample value of a sample, thus thereplaced sample value is used as a reference sample of the currentblock.

FIG. 7 is a diagram illustrating reference samples capable of being usedfor intra prediction.

As shown in FIG. 7, at least one of the reference sample line 0 to thereference sample line 3 may be used for intra prediction of the currentblock. In FIG. 7, the samples of a segment A and a segment F may bepadded with the samples closest to a segment B and a segment E,respectively, instead of retrieving from the reconstructed neighboringblock. Index information indicating the reference sample line to be usedfor intra prediction of the current block may be signaled. For example,in FIG. 7, reference sample line indicators 0, 1, and 2 may be signaledas index information indicating reference sample lines 0, 1 and 2. Whenthe upper boundary of the current block is the boundary of the CTU, onlythe reference sample line 0 may be available. Therefore, in this case,the index information may not be signaled. When a reference sample lineother than the reference sample line 0 is used, filtering for aprediction block, which will be described later, may not be performed.

When intra-predicting, a filter may be applied to at least one of areference sample and a prediction sample based on an intra-predictionmode and a current block size.

In case of a planar mode, when generating a prediction block of acurrent block, according to a position of a prediction target samplewithin a prediction block, a sample value of the prediction targetsample may be generated by using a weighted sum of an upper and leftside reference sample of a current block, and a right upper side andleft lower side reference sample of the current block. In addition, incase of a DC mode, when generating a prediction block of a currentblock, an average value of upper side and left side reference samples ofthe current block may be used. In addition, in case of an angular mode,a prediction block may be generated by using an upper side, a left side,a right upper side, and/or a left lower side reference sample of thecurrent block. In order to generate a prediction sample value,interpolation of a real number unit may be performed.

In the case of intra prediction between color components, a predictionblock for the current block of the second color component may begenerated on the basis of the corresponding reconstructed block of thefirst color component. For example, the first color component may be aluma component, and the second color component may be a chromacomponent. For intra prediction between color components, the parametersof the linear model between the first color component and the secondcolor component may be derived on the basis of the template. Thetemplate may include upper and/or left neighboring samples of thecurrent block and upper and/or left neighboring samples of thereconstructed block of the first color component corresponding thereto.For example, the parameters of the linear model may be derived using asample value of a first color component having a maximum value amongsamples in a template and a sample value of a second color componentcorresponding thereto, and a sample value of a first color componenthaving a minimum value among samples in the template and a sample valueof a second color component corresponding thereto. When the parametersof the linear model are derived, a corresponding reconstructed block maybe applied to the linear model to generate a prediction block for thecurrent block. According to a video format, subsampling may be performedon the neighboring samples of the reconstructed block of the first colorcomponent and the corresponding reconstructed block. For example, whenone sample of the second color component corresponds to four samples ofthe first color component, four samples of the first color component maybe sub-sampled to compute one corresponding sample. In this case, theparameter derivation of the linear model and intra prediction betweencolor components may be performed on the basis of the correspondingsub-sampled samples. Whether or not to perform intra prediction betweencolor components and/or the range of the template may be signaled as theintra prediction mode.

The current block may be partitioned into two or four sub-blocks in thehorizontal or vertical direction. The partitioned sub-blocks may besequentially reconstructed. That is, the intra prediction may beperformed on the sub-block to generate the sub-prediction block. Inaddition, dequantization and/or inverse transform may be performed onthe sub-blocks to generate sub-residual blocks. A reconstructedsub-block may be generated by adding the sub-prediction block to thesub-residual block. The reconstructed sub-block may be used as areference sample for intra prediction of the sub-sub-blocks. Thesub-block may be a block including a predetermined number (for example,16) or more samples. Accordingly, for example, when the current block isan 8×4 block or a 4×8 block, the current block may be partitioned intotwo sub-blocks. Also, when the current block is a 4×4 block, the currentblock may not be partitioned into sub-blocks. When the current block hasother sizes, the current block may be partitioned into four sub-blocks.Information on whether or not to perform the intra prediction based onthe sub-blocks and/or the partitioning direction (horizontal orvertical) may be signaled. The intra prediction based on the sub-blocksmay be limited to be performed only when reference sample line 0 isused. When the intra prediction based on the sub-block is performed,filtering for the prediction block, which will be described later, maynot be performed.

The final prediction block may be generated by performing filtering onthe prediction block that is intra-predicted. The filtering may beperformed by applying predetermined weights to the filtering targetsample, the left reference sample, the upper reference sample, and/orthe upper left reference sample. The weight and/or the reference sample(range, position, etc.) used for the filtering may be determined on thebasis of at least one of a block size, an intra prediction mode, and aposition of the filtering target sample in the prediction block. Thefiltering may be performed only in the case of a predetermined intraprediction mode (e.g., DC, planar, vertical, horizontal, diagonal,and/or adjacent diagonal modes). The adjacent diagonal mode may be amode in which k is added to or subtracted from the diagonal mode. Forexample, k may be a positive integer of 8 or less.

An intra-prediction mode of a current block may be entropyencoded/decoded by predicting an intra-prediction mode of a blockpresent adjacent to the current block. When intra-prediction modes ofthe current block and the neighbor block are identical, information thatthe intra-prediction modes of the current block and the neighbor blockare identical may be signaled by using predetermined flag information.In addition, indicator information of an intra-prediction mode that isidentical to the intra-prediction mode of the current block amongintra-prediction modes of a plurality of neighbor blocks may besignaled. When intra-prediction modes of the current block and theneighbor block are different, intra-prediction mode information of thecurrent block may be entropy encoded/decoded by performing entropyencoding/decoding based on the intra-prediction mode of the neighborblock.

FIG. 5 is a diagram illustrating an embodiment of an inter-pictureprediction process.

In FIG. 5, a rectangle may represent a picture. In FIG. 5, an arrowrepresents a prediction direction. Pictures may be categorized intointra pictures (I pictures), predictive pictures (P pictures), andBi-predictive pictures (B pictures) according to the encoding typethereof.

The I picture may be encoded through intra-prediction without requiringinter-picture prediction. The P picture may be encoded throughinter-picture prediction by using a reference picture that is present inone direction (i.e., forward direction or backward direction) withrespect to a current block. The B picture may be encoded throughinter-picture prediction by using reference pictures that are preset intwo directions (i.e., forward direction and backward direction) withrespect to a current block. When the inter-picture prediction is used,the encoder may perform inter-picture prediction or motion compensationand the decoder may perform the corresponding motion compensation.

Hereinbelow, an embodiment of the inter-picture prediction will bedescribed in detail.

The inter-picture prediction or motion compensation may be performedusing a reference picture and motion information.

Motion information of a current block may be derived duringinter-picture prediction by each of the encoding apparatus 100 and thedecoding apparatus 200. The motion information of the current block maybe derived by using motion information of a reconstructed neighboringblock, motion information of a collocated block (also referred to as acol block or a co-located block), and/or a block adjacent to theco-located block. The co-located block may mean a block that is locatedspatially at the same position as the current block, within a previouslyreconstructed collocated picture (also referred to as a col picture or aco-located picture). The co-located picture may be one picture among oneor more reference pictures included in a reference picture list.

The derivation method of the motion information may be differentdepending on the prediction mode of the current block. For example, aprediction mode applied for inter prediction includes an AMVP mode, amerge mode, a skip mode, a merge mode with a motion vector difference, asubblock merge mode, a geometric partitioning mode, an combined interintra prediction mode, affine mode, and the like. Herein, the merge modemay be referred to as a motion merge mode.

For example, when the AMVP is used as the prediction mode, at least oneof motion vectors of the reconstructed neighboring blocks, motionvectors of the co-located blocks, motion vectors of blocks adjacent tothe co-located blocks, and a (0, 0) motion vector may be determined asmotion vector candidates for the current block, and a motion vectorcandidate list is generated by using the emotion vector candidates. Themotion vector candidate of the current block can be derived by using thegenerated motion vector candidate list. The motion information of thecurrent block may be determined based on the derived motion vectorcandidate. The motion vectors of the collocated blocks or the motionvectors of the blocks adjacent to the collocated blocks may be referredto as temporal motion vector candidates, and the motion vectors of thereconstructed neighboring blocks may be referred to as spatial motionvector candidates.

The encoding apparatus 100 may calculate a motion vector difference(MVD) between the motion vector of the current block and the motionvector candidate and may perform entropy encoding on the motion vectordifference (MVD). In addition, the encoding apparatus 100 may performentropy encoding on a motion vector candidate index and generate abitstream. The motion vector candidate index may indicate an optimummotion vector candidate among the motion vector candidates included inthe motion vector candidate list. The decoding apparatus may performentropy decoding on the motion vector candidate index included in thebitstream and may select a motion vector candidate of a decoding targetblock from among the motion vector candidates included in the motionvector candidate list by using the entropy-decoded motion vectorcandidate index. In addition, the decoding apparatus 200 may add theentropy-decoded MVD and the motion vector candidate extracted throughthe entropy decoding, thereby deriving the motion vector of the decodingtarget block.

Meanwhile, the coding apparatus 100 may perform entropy-coding onresolution information of the calculated MVD. The decoding apparatus 200may adjust the resolution of the entropy-decoded MVD using the MVDresolution information.

Meanwhile, the coding apparatus 100 calculates a motion vectordifference (MVD) between a motion vector and a motion vector candidatein the current block on the basis of an affine model, and performsentropy-coding on the MVD. The decoding apparatus 200 derives a motionvector on a per sub-block basis by deriving an affine control motionvector of a decoding target block through the sum of the entropy-decodedMVD and an affine control motion vector candidate.

The bitstream may include a reference picture index indicating areference picture. The reference picture index may be entropy-encoded bythe encoding apparatus 100 and then signaled as a bitstream to thedecoding apparatus 200. The decoding apparatus 200 may generate aprediction block of the decoding target block based on the derivedmotion vector and the reference picture index information.

Another example of the method of deriving the motion information of thecurrent may be the merge mode. The merge mode may mean a method ofmerging motion of a plurality of blocks. The merge mode may mean a modeof deriving the motion information of the current block from the motioninformation of the neighboring blocks. When the merge mode is applied,the merge candidate list may be generated using the motion informationof the reconstructed neighboring blocks and/or the motion information ofthe collocated blocks. The motion information may include at least oneof a motion vector, a reference picture index, and an inter-pictureprediction indicator. The prediction indicator may indicateone-direction prediction (L0 prediction or L1 prediction) ortwo-direction predictions (L0 prediction and L1 prediction).

The merge candidate list may be a list of motion information stored. Themotion information included in the merge candidate list may be at leastone of motion information (spatial merge candidate) of a neighboringblock adjacent to the current block, motion information (temporal mergecandidate) of the collocated block of the current block in the referencepicture, new motion information generated by a combination of the motioninformation exiting in the merge candidate list, motion information(history-based merge candidate) of the block that is encoded/decodedbefore the current block, and zero merge candidate.

The encoding apparatus 100 may generate a bitstream by performingentropy encoding on at least one of a merge flag and a merge index andmay signal the bitstream to the decoding apparatus 200. The merge flagmay be information indicating whether or not to perform the merge modefor each block, and the merge index may be information indicating thatwhich neighboring block, among the neighboring blocks of the currentblock, is a merge target block. For example, the neighboring blocks ofthe current block may include a left neighboring block on the left ofthe current block, an upper neighboring block disposed above the currentblock, and a temporal neighboring block temporally adjacent to thecurrent block.

Meanwhile, the coding apparatus 100 performs entropy-coding on thecorrection information for correcting the motion vector among the motioninformation of the merge candidate and signals the same to the decodingapparatus 200. The decoding apparatus 200 can correct the motion vectorof the merge candidate selected by the merge index on the basis of thecorrection information. Here, the correction information may include atleast one of information on whether or not to perform the correction,correction direction information, and correction size information. Asdescribed above, the prediction mode that corrects the motion vector ofthe merge candidate on the basis of the signaled correction informationmay be referred to as a merge mode having the motion vector difference.

The skip mode may be a mode in which the motion information of theneighboring block is applied to the current block as it is. When theskip mode is applied, the encoding apparatus 100 may perform entropyencoding on information of the fact that the motion information of whichblock is to be used as the motion information of the current block togenerate a bit stream, and may signal the bitstream to the decodingapparatus 200. The encoding apparatus 100 may not signal a syntaxelement regarding at least any one of the motion vector differenceinformation, the encoding block flag, and the transform coefficientlevel to the decoding apparatus 200.

The subblock merge mode may mean a mode that derives the motioninformation in units of sub-blocks of a coding block (CU). When thesubblock merge mode is applied, a subblock merge candidate list may begenerated using motion information (sub-block based temporal mergecandidate) of the sub-block collocated to the current sub-block in thereference image and/or an affine control point motion vector mergecandidate.

The geometric partitioning mode may mean a mode that derives motioninformation by partitioning the current block into the predefineddirections, derives each prediction sample using each of the derivedmotion information, and derives the prediction sample of the currentblock by weighting each of the derived prediction samples.

The inter-intra combined prediction mode may mean a mode that derives aprediction sample of the current block by weighting a prediction samplegenerated by inter prediction and a prediction sample generated by intraprediction.

The decoding apparatus 200 may correct the derived motion information byitself. The decoding apparatus 200 may search the predetermined regionon the basis of the reference block indicated by the derived motioninformation and derive the motion information having the minimum SAD asthe corrected motion information.

The decoding apparatus 200 may compensate a prediction sample derivedvia inter prediction using an optical flow.

FIG. 6 is a diagram illustrating a transform and quantization process.

As illustrated in FIG. 6, a transform and/or quantization process isperformed on a residual signal to generate a quantized level signal. Theresidual signal is a difference between an original block and aprediction block (i.e., an intra prediction block or an inter predictionblock). The prediction block is a block generated through intraprediction or inter prediction. The transform may be a primarytransform, a secondary transform, or both. The primary transform of theresidual signal results in transform coefficients, and the secondarytransform of the transform coefficients results in secondary transformcoefficients.

At least one scheme selected from among various transform schemes whichare preliminarily defined is used to perform the primary transform. Forexample, examples of the predefined transform schemes include discretecosine transform (DCT), discrete sine transform (DST), andKarhunen-Loève transform (KLT). The transform coefficients generatedthrough the primary transform may undergo the secondary transform. Thetransform schemes used for the primary transform and/or the secondarytransform may be determined according to coding parameters of thecurrent block and/or neighboring blocks of the current block.Alternatively, transform information indicating the transform scheme maybe signaled. The DCT-based transform may include, for example, DCT-2,DCT-8, and the like. The DST-based transform may include, for example,DST-7.

A quantized-level signal (quantization coefficients) may be generated byperforming quantization on the residual signal or a result of performingthe primary transform and/or the secondary transform. The quantizedlevel signal may be scanned according to at least one of a diagonalup-right scan, a vertical scan, and a horizontal scan, depending on anintra prediction mode of a block or a block size/shape. For example, asthe coefficients are scanned in a diagonal up-right scan, thecoefficients in a block form change into a one-dimensional vector form.Aside from the diagonal up-right scan, the horizontal scan ofhorizontally scanning a two-dimensional block form of coefficients orthe vertical scan of vertically scanning a two-dimensional block form ofcoefficients may be used depending on the intra prediction mode and/orthe size of a transform block. The scanned quantized-level coefficientsmay be entropy-encoded to be inserted into a bitstream.

A decoder entropy-decodes the bitstream to obtain the quantized-levelcoefficients. The quantized-level coefficients may be arranged in atwo-dimensional block form through inverse scanning. For the inversescanning, at least one of a diagonal up-right scan, a vertical scan, anda horizontal scan may be used.

The quantized-level coefficients may then be dequantized, then besecondary-inverse-transformed as necessary, and finally beprimary-inverse-transformed as necessary to generate a reconstructedresidual signal.

Inverse mapping in a dynamic range may be performed for a luma componentreconstructed through intra prediction or inter prediction beforein-loop filtering. The dynamic range may be divided into 16 equal piecesand the mapping function for each piece may be signaled. The mappingfunction may be signaled at a slice level or a tile group level. Aninverse mapping function for performing the inverse mapping may bederived on the basis of the mapping function. In-loop filtering,reference picture storage, and motion compensation are performed in aninverse mapped region, and a prediction block generated through interprediction is converted into a mapped region via mapping using themapping function, and then used for generating the reconstructed block.However, since the intra prediction is performed in the mapped region,the prediction block generated via the intra prediction may be used forgenerating the reconstructed block without mapping/inverse mapping.

When the current block is a residual block of a chroma component, theresidual block may be converted into an inverse mapped region byperforming scaling on the chroma component of the mapped region. Theavailability of the scaling may be signaled at the slice level or thetile group level. The scaling may be applied only when the mapping forthe luma component is available and the division of the luma componentand the division of the chroma component follow the same tree structure.The scaling may be performed on the basis of an average of sample valuesof a luma prediction block corresponding to the color difference block.In this case, when the current block uses inter prediction, the lumaprediction block may mean a mapped luma prediction block. A valuenecessary for the scaling may be derived by referring to a lookup tableusing an index of a piece to which an average of sample values of a lumaprediction block belongs. Finally, by scaling the residual block usingthe derived value, the residual block may be switched to the inversemapped region. Then, chroma component block restoration, intraprediction, inter prediction, in-loop filtering, and reference picturestorage may be performed in the inverse mapped area.

Information indicating whether the mapping/inverse mapping of the lumacomponent and chroma component is available may be signaled through aset of sequence parameters.

The prediction block of the current block may be generated on the basisof a block vector indicating a displacement between the current blockand the reference block in the current picture. In this way, aprediction mode for generating a prediction block with reference to thecurrent picture is referred to as an intra block copy (IBC) mode. TheIBC mode may be applied to M×N (M<=64, N<=64) coding units. The IBC modemay include a skip mode, a merge mode, an AMVP mode, and the like. Inthe case of a skip mode or a merge mode, a merge candidate list isconstructed, and the merge index is signaled so that one merge candidatemay be specified. The block vector of the specified merge candidate maybe used as a block vector of the current block. The merge candidate listmay include at least one of a spatial candidate, a history-basedcandidate, a candidate based on an average of two candidates, and azero-merge candidate. In the case of an AMVP mode, the difference blockvector may be signaled. In addition, the prediction block vector may bederived from the left neighboring block and the upper neighboring blockof the current block. The index on which neighboring block to use may besignaled. The prediction block in the IBC mode is included in thecurrent CTU or the left CTU and limited to a block in the alreadyreconstructed area. For example, a value of the block vector may belimited such that the prediction block of the current block ispositioned in an area of three 64x64 blocks preceding the 64×64 block towhich the current block belongs in the coding/decoding order. Bylimiting the value of the block vector in this way, memory consumptionand device complexity according to the IBC mode implementation may bereduced.

Hereinafter, a coding/decoding method using subpicture merging and substream extraction according to embodiments of the present disclosure.

FIG. 8 is a view illustrating an image coding/decoding method accordingto an embodiment of the present disclosure.

Referring to FIG. 8, the image coding/decoding method according to theembodiment of the present disclosure may include partitioning a currentpicture into a plurality of subpictures (S810), obtaining subpictureinformation of the partitioned subpictures (S820) and/or generating asingle stream for a current picture by merging the obtained subpictureinformation (S830).

FIG. 9 is a view illustrating an image coding/decoding method accordingto another embodiment of the present disclosure.

Referring to FIG. 9, the image coding/decoding method according toanother embodiment of the present disclosure may include obtaining asingle stream including subpicture information of a plurality ofsubpictures (S910), selecting a subpicture to be extracted from amongthe plurality of subpictures (S920), determining a single stream as astream to be extracted (S930) and/or obtaining a sub stream for thesubpicture to be extracted from the stream to be extracted, by removingor using at least one piece of sub picture information included in thestream to be extracted (S940).

The stream may mean a bitstream. In addition, the single stream mayinclude at least one sub stream. In addition, the sub steam may beextracted from the single stream and may include coded information of apredetermined region in one picture.

Hereinafter, a detailed configuration applicable to FIGS. 8 and 9 willbe described in detail.

According to the configuration of FIG. 8, one picture may be partitionedinto at least one subpicture to obtain a single stream compatible withor conforming to coded sub streams. For parallel processing andindividual coding/decoding of a predetermined region unit in onepicture, subpicture information of the partitioned subpictures may becoded/decoded in units of subpictures. That is, at least one of thesubpicture information of the subpictures may be merged, therebygenerating a single stream for a picture. At this time, singlecoding/decoding may be performed.

According to the configuration of FIG. 9, when a specific sub stream isextracted from the merged single stream, a sub stream compatible with orconforming to a coder/decoder may be extracted. For individualcoding/decoding of the predetermined region unit in one picture, atleast one piece of subpicture information may be extracted from a singlestream including subpicture information of the plurality of subpictures,thereby generating a sub stream including at least one piece of subpicture information. At this time, the sub stream may be individuallycoded/decoded without depending on other sub streams in thecoder/decoder.

One picture included in an image may be partitioned into one or moresubpictures and the image may be coded/decoding in units of subpictures.

A parameter set or header (e.g., SPS or PPS) of a coded stream (codedvideo sequence (CVS)) may include at least one of the following subpicture information. For example, the subpicture information may includeat least one of information indicating the number of subpicturesincluded in one picture, location information of each subpicture in onepicture, size information of each subpicture in one picture, informationindicating whether parsing and encoding of a subpicture is performed inthe same manner as one picture, subpicture filtering information,information indicating whether the number of subpictures is equal to orgreater than 2, information indicating the index of a subpicturecorresponding to a grid, information indicating whether a subpicture iscapable of being coded/decoded like a picture, information on a CTUlocated at a top left side of the subpicture or subpicture IDinformation. In addition, the subpicture information may include atleast one of video coding layer (VCL) network abstraction layer (NAL)unit or a non-VCL NAL unit of a subpicture.

Meanwhile, the subpicture may include one or more CTU rows or one ormore CTU columns, and the size of the subpicture may be signaled basedon the width and height of a CTU unit or the width and height of apredetermined block unit.

For example, subpicture filtering information may include informationindicating whether at least one of a deblocking filter, a sampleadaptive offset (SAO) or an adaptive loop filter (ALF) is applied to aboundary between subpictures.

The subpicture may be composed of at least one slice/tile and may beexpressed as one or more VCL NAL units on a stream. Here, the sub VCLNAL unit may include coded video information. For example, at least oneof coded picture/subpicture/slice/tile information may be included. Atthis time, the slice header of each subpicture may include at least oneof the following information. For example, a subpicture identifierindicating what numberth of a current picture a current subpicture isand an identifier for identifying header information of the subpicturemay be included in a slice header.

For example, the identifier indicating what numberth of a currentpicture a current subpicture is may be defined as a syntax elementsub_pic_idx.

For example, the identifier for identifying the header information ofthe subpicture may identify a parameter set or header informationnecessary to decode the subpicture.

For example, VCL NAL units of each subpicture may be signaled accordingto the raster scan order. In another example, the VCL NAL units of eachsubpicture may be signaled according to ascending order of subpictureidentifier sub_pic_idx.

FIG. 10 is a view illustrating a subpicture included in one picture, andFIG. 11 is a view illustrating a stream including a plurality ofsubpictures.

FIG. 10 shows an example of partitioning one picture into ninesubpictures. For example, the picture may be partitioned intorectangular subpictures. FIG. 11 shows an example of a stream in whichinformation on nine subpictures is compressed and included. As describedabove, subpictures may be included in a stream and signaled according tothe raster scan order.

Each subpicture may be coded/decoded by an independent coder/decoder. Inthis case, since each coder/decoder may consider a subpicture as onepicture and perform coding/decoding, one subpicture composed of one ormore VCL NAL units may be coded/decoded in access units (AUs).Accordingly, the following non-VCL NAL units may be coded/decoded beforeor after a stream of subpictures.

In the following description, the stream of subpictures may mean a substream. In addition, coding/decoding before the stream of the subpicturemay mean that coding/encoding is performed earlier than the subpictureand coding/decoding after the stream of the subpicture may mean thatcoding/decoding is performed later than the subpicture.

Meanwhile, the non-VCL NAL unit may include information other than codedvideo information. For example, at least one of a video parameter set, asequence parameter set, a picture parameter set, an adaptive parameterset, a picture header, an access unit delimiter (AUD), filter data (FD)or supplemental enhancement information (SEI) may be included.

For example, the following non-VCL NAL units may be signaled before thefirst VCL NAL unit of the subpicture and information on the non-VCL NALunit may be used as information on the subpicture.

-   -   AUD    -   Prefix SEI

The following non-VCL NAL units may be signaled after the last VCL NALunit of the subpicture and information on the non-VCL NAL unit may beused as information on the subpicture.

-   -   Suffix SEI    -   FD

The NAL unit header or raw byte sequence payload (RBSP) of the non-VCLNAL units may include the identifier indicating what numberth of acurrent picture a current subpicture is. Here, the RBSP may mean asyntax structure including a syntax element and may include at least oneof a parameter set, a header or coded picture/subpicture/slice/tileinformation.

An AU boundary may be identified using information slice_addressindicating what numberth of a subpicture a current slice included in aAUD, Prefix SEI, Suffix SEI or slice header is.

For example, a coding apparatus may signal an AUD before coding asubpicture. A decoding apparatus may recognize that a new AU starts whenreceiving the AUD.

FIG. 12 is a view illustrating a stream structure of a sub pictureaccess unit (AU).

FIG. 12 shows an example in which a subpicture composed of three slicesVCL NAL #1, VCL NAL #2 and VCL NAL #3 is signaled through a singlestream composed of two AUs. The start boundary of a first AU may bedetermined using the AUD and the end boundary of the AU may bedetermined using at least one of Suffix SEI or slice_address of theslice header of a next AU.

Sub streams of subpictures may be merged into a single streamconfiguring one picture and signaled. When one or more sub streams aremerged into a single stream, a new non-VCL NAL unit may be added.

Unmerged sub streams may be independently coded/decoded. At least one ofAUD or Prefix SEI may be signaled before each AU and at least one ofSuffix SEI or FD may be signaled after each AU. When one or more substreams are merged to generate a stream for one picture, a non-VCL NALunit or SEI for identifying an AU boundary may be inserted into thestream.

FIG. 13 is a view illustrating a syntax element structure of an AUD.

An AUD indicating an AU boundary of a picture unit may be inserted intoa stream. When the stream is merged, an AUD indicating the boundary of apicture unit AU may be added before each AU of a sub streamcorresponding to a first subpicture.

For example, when the sub stream is merged, AUD RBSP may be signaled. Atthis time, a syntax element pic_aud_flag or aud_irap_or_gdr_flag havinga first value for identifying the boundary of the AU for a picture(which is not a subpicture) may be included in the AUD RBSP. Here, thefirst value may mean 1 and the boundary of the AU when pic_aud_flag oraud_irap_or_gdr_flag indicates the first value may mean a pictureboundary.

FIGS. 14 and 15 are views illustrating a stream structure of a pictureAU.

FIGS. 14 and 15 shows examples in which an AUD is used when two substreams for two subpictures are merged to generate a single stream forone picture. FIG. 14 shows two unmerged sub streams and FIG. 15 shows amerged single stream. As shown in FIG. 15, an AUD with pic_aud_flaghaving a first value may be added before a first sub stream, therebydetermining the boundary of the picture AU. That is, when there is anAUD with pic_aud_flag having a first value, it may be determined as theboundary of the picture AU. In the following description, the picture AUmay be expressed as PicAU and the subpicture AU may be expressed asSubAU.

FIG. 16 is another view illustrating a stream structure of a picture AU.

FIG. 16 shows an example in which Prefix SEI for identifying PicAU isinserted into a single stream when sub streams are merged.

For example, when a single stream for one picture is generated bymerging at least two sub streams, Prefix SEI meaning the boundary ofPicAU may be inserted into the stream. When the sub streams are merged,Prefix SEI having a payload type indicating the PicAU boundary may beinserted before each SubAU of the sub stream corresponding to a firstsubpicture. A decoder may determine that a new AU starts when Prefix SEIhaving the payload type is signaled in a single stream. Here,determining that the new AU starts may mean that the boundary of thepicture AU is determined. That is, when there is Prefix SEI having thepayload type indicating the PicAU boundary, this may be determined asthe boundary of the picture AU.

In another example, when sub streams are merged, an end of bitstream(EOB) NAL unit indicating the end of the single stream may be insertedat the end of the merged stream. At this time, in order to distinguishbetween the EOB of the sub stream and the EOB of the single stream, theEOB having a different NAL unit type from the EOB which may be used inthe sub stream may be inserted at the end of the PicAU.

The decoder may identify the picture AU in the single stream in whichsub streams are merged using at least one of the above-describedmethods.

When one or more sub streams are merged into a single stream, a specificnon-VCL NAL unit included in a sub stream may be removed or changed.That is, at least one of the following non-VCL NAL units may be removedor changed when sub streams are merged into a single stream. Forexample, the removed or changed NAL unit may be at least one of adecoding parameter set (DPS), a video parameter set (VPS), an end ofbitstream (EOB), an end of sequence (EOS), an access unit delimiter(AUD), a sequence parameter set (SPS), a picture parameter set (PPS) orsub picture info supplemental enhancement information (SEI).

For example, when DPSs are respectively included in sub streams and thesub streams are merged, all DPSs included in the sub streams other thana DPS included in one sub stream may be removed. In another example, onthe assumption that all syntax elements in the DPSs included in the substreams have the same value, all the DPSs of the sub streams may beremoved and only one DPS may be inserted into the single stream. Forexample, the DPS may be inserted before the first sub stream in thesingle stream.

In another example, when VPSs are respectively included in sub streamsand the sub streams are merged, all VPSs included in the sub streamsother than a VPS included in one sub stream may be removed. In anotherexample, on the assumption that all syntax elements in the VPSs includedin the sub streams have the same value, all the VPSs of the sub streamsmay be removed and only one VPS may be inserted into the single stream.For example, the VPS may be inserted before the first sub stream in thesingle stream.

In another example, when EOSs are respectively included in sub streamsand the sub streams are merged, all EOSs included in the sub streamsother than an EOS included in one sub stream may be removed. In anotherexample, on the assumption that all the EOSs included in the sub streamsare respectively located after SubAUs of the sub streams, all the EOSsof the sub streams may be removed and only one EOS may be inserted afterPicAU in the single stream.

In another example, on the assumption that all the EOSs respectivelyincluded in the sub streams are respectively located after n-th SubAUsof the sub streams, all the EOSs of the sub streams may be removed andonly one EOS may be inserted after the N-th PicAU in the single stream.

In another example, when EOBs are respectively included in sub streamsand the sub streams are merged, all EOBs included in the sub streamsother than an EOB included in one sub stream may be removed. In anotherexample, all the EOBs of the sub streams may be removed and only one EOBmay be inserted into the single stream. For example, the EOB may beinserted after the last sub stream in the single stream.

In another example, when AUDs are respectively included in sub streamsand the sub streams are merged, all AUDs included in the sub streamsother than an AUD included in one sub stream may be removed.Alternatively, when the sub streams are merged, the AUD may beinserted/maintained only before the sub stream corresponding to thefirst subpicture in the picture. That is, all the AUDs other than theAUD located before the sub stream corresponding to the first subpicturein the picture may be removed.

In another example, when SPSs are respectively included in sub streamsand the sub streams are merged, all SPSs included in the sub streams maybe removed and a new SPS including information on the subpicturesincluded in the single stream may be generated and inserted into themerged single stream. For example, the SPS may be inserted before asequence in the single stream. For example, information on thesubpictures may be at least one of the following syntax elements.

The syntax element subpics_present_flag may indicate whether the numberof subpictures to be merged is two or more. For example, when the numberof subpictures is two or more, subpics_present_flag may have 1 which isa first value. In addition, subpics_present_flag may indicate whethersubpicture information is present. For example, whensubpics_present_flag is 1 which is the first value, the subpictureinformation may be present and, when subpics_present_flag is 0 which isa second value, the subpicture information may not be present in thestream.

A syntax element max_subpics_minus1 may indicate a value obtained bysubtracting 1 from the number of merged subpictures. That is,max_subpics_minus1 may mean information indicating the number ofsubpictures included in one picture.

A syntax element subpic_grid_idx may indicate the index of a subpicturecorresponding to each grid when a picture is partitioned into arbitrarygrids (e.g., 4×4). Meanwhile, size information (e.g., width/height,resolution, etc.) of the subpicture included in the SPS of each substream may be used to derive subpic_grid_idx.

A syntax element subpic_treated_as_pic_flag may indicate whether eachsubpicture is capable of being coded/decoded like the picture.

In another example, when PPSs are respectively included in sub streamsand the sub streams are merged, all

PPSs included in the sub streams other than an PPS included in one substream may be removed. In another example, on the assumption that allsyntax elements in the PPSs included in each sub stream have the samevalue, all the PPSs of the sub streams may be removed and only one PPSmay be inserted into the single stream. For example, the PPS may beinserted before the first sub stream in the single stream.

In another example, when sub picture info SEI is included in sub streamsand the sub streams are merged, all sub picture info SEI included in thesub streams other than sub picture info SEI included in one sub streammay be removed. In another example, the sub picture info SEIcorresponding to each merged subpicture information may be inserted intothe single stream. For example, the sub picture info SEI may be insertedafter the last sub stream in the single stream.

FIG. 17 is a view illustrating an example of merging sub streams togenerate a single stream.

When sub streams are merged into a single stream, the location of aspecific non-VCL NAL unit included in the sub stream may be moved in thesingle stream.

For example, when Prefix SEI is included in a sub stream, Prefix SEI maybe moved to the front side of a first VCL NAL unit of a first subpictureof the single stream PicAU. FIG. 17 shows an example in which, when boththe same N-th SubAUs of two sub streams include Prefix SEI, the substreams are merged into a single stream. When being merged into thesingle stream, one or more Prefix SEI included in the same N-th SubAU ofeach sub stream may be moved to the front side of a first VCL NAL unitof the sub stream for the first subpicture in the single stream. Inaddition, the order of Prefix SEI may be aligned in the same manner assub picture indices.

In another example, when Suffix SEI is included in a sub stream, SuffixSEI may be moved to the back side of the last VCL NAL unit of the lastsub picture of the single stream PicAU. At this time, when there are oneor more pieces of Suffix SEI, the Suffix SEI may be aligned in the samemanner as sub picture indices.

When one or more sub streams are merged into a single stream, Prefix SEIincluded in the sub streams may be moved to the front side of the firstVLC NAL unit for the sub picture. That is, within the merged singlestream PicAU, the Prefix SEI may be present between VLC NALs, and therange of application of each Prefix SEI may be defined as a currentSubAU.

For example, when recovery point SEI is present in the merged singlestream, the range of application of SEI may be limited to the currentSubAU. That is, SEI is applicable to only the sub picture correspondingto the current SubAU.

When one or more sub streams are merged into a single stream, Suffix SEIincluded in the sub streams may be moved to the back side of the lastVLC NAL unit for the sub picture. That is, within the merged singlestream PicAU, the Suffix SEI may be present between VLC NALs, and therange of application of each Suffix SEI may be defined as a currentSubAU.

For example, when decoded_picture_hash SEI is present in the mergedsingle stream, the range of application of SEI may be limited to thecurrent SubAU. That is, SEI is applicable to only the sub picturecorresponding to the current SubAU.

When the sub stream for one or more subpictures is extracted from thesignaled single stream, specific non-VCL NAL units may be removed orchanged.

In the embodiments of the present disclosure, the sub stream may beobtained by setting a single stream as a stream to be extracted andremoving unnecessary information from the stream to be extracted orchanging some information of the stream to be extracted.

A coder/decoder may derive a final sub stream by removing unnecessaryinformation from the derived single stream or changing some information.

For example, when the maximum temporal layer identifier tIdTarget valueof the NAL unit included in the stream to be extracted is greater thanthe temporal layer identifier TemporalId, to which current streamextraction is applied, the NAL units may be removed from the stream tobe extracted. That is, when TemporalId is greater than tIdTarget, theNAL units may be removed from the stream to be extracted.

In another example, when the NAL units included in the stream to beextracted satisfy a predetermined condition, the NAL units may beremoved from the stream to be extracted.

In another example, when Non-VCL NAL unit or SEI inserted in order toidentify the PicAU boundary is present in the stream to be extracted dueto merging, a sub stream, from which the non-VCL NAL unit or SEI isremoved, may be extracted.

In another example, when there is an AUD for identifying the PicAUboundary, the sub stream may be extracted by removing the AUD orchanging the value of the syntax element aud_irap_or_gdr_flag valueindicating the picture unit boundary included in the AUD to a secondvalue meaning SubAU. At this time, the second value may be 0.

In another example, SPS information for pictures included in the singlestream may be changed to SPS information of the extracted sub pictures.For example, SPS information may be changed as follows.

Since a syntax element subpics_present_flag indicates the number ofsubpictures present in a sequence, when the number of extractedsubpictures is 1, it may be changed to 0 which is a second value.

A syntax element max_subpics_minus1 may be changed to a value of thenumber of extracted subpictures −1. That is, max_subpics_minus1 may bechanged to 0 and extracted in order to indicate that only one subpictureor picture is present.

A syntax element subpic_grid_idx may be changed to the index of asubpicture corresponding to each grid, when the extracted subpicturesare regarded as one picture and partitioned into arbitrary grids (e.g.,4×4).

Syntax elements sps_subpic_ctu_top_left_x and sps_subpic_ctu_top_left_ymean the coordinates of a CTU located at the top left side, theextracted subpictures may be considered as one picture and thussps_subpic_ctu_top_left_x and sps_subpic_ctu_top_left_y may be changedto 0.

The width information and height information of the picture in SPSinformation may be changed to the width information and heightinformation of a subpicture.

For example, when the arbitrary grid is a CTU, the SPS information ofthe subpictures may be located after log 2_ctu_size_minus5.

In another example, when SPS information of a plurality of subpicturesis present in a single stream, the SPS information of the extractedsubpicture may be extracted using information on the subpicture or thesingle stream, and the SPS information of the remaining subpictures maybe removed.

The SPS information of the extracted subpicture may be changed andextracted or may be extracted based on the SPS information of the singlestream. For example, when only one subpicture is extracted, thecoordinates (sps_subpic_ctu_top_left_x, sps_subpic_ctu_top_left_y) ofthe CTU located at the top left side of the extracted subpicture may bechanged to (0, 0) and extracted. In addition, informationsps_num_subpics_minus1 indicating the total number of subpictures may bechanged to 0 and extracted. That is, the total number of subpictures maybe set to 1. In addition, the width information and height informationof the picture in the SPS information may be changed to the widthinformation and height information of the subpicture and extracted.

On the other hand, at least one of information indicating whether totreat a subpicture as a picture sps_subpic_treated_as_pic_flag,information indicating whether to apply a filter for a subpictureboundary sps_loop_filter_across_subpic_enabled_flag or a subpicture IDsps_subpic_id may be extracted without change. Here, the informationindicating whether to treat the subpicture as the picture may meaninformation indicating whether parsing or decoding of a subpicture isperformed in the same manner as one picture. In addition, informationindicating whether to apply the filter for the subpicture boundary maymean subpicture filtering information.

Meanwhile, at least one of sps_subpic_ctu_top_left_x,sps_subpic_ctu_top_left_y, sps_subpic_width_minus1,sps_subpic_height_minus1, sps_subpic_treated_as_pic_flag,sps_loop_filter_across_subpic_enabled_flag or sps_subpic_id of anunextracted subpicture may be removed when the subpicture is extracted.

In another example, when PPS information of a plurality of subpicturesis present in a single stream, the PPS information of an extractedsubpicture may be extracted using information on the subpicture or thesingle stream and PPS information of the remaining subpictures may beremoved.

For example, information indicating the total number of subpicturespps_num_subpics_minus1 may be changed to 0 and extracted. That is, thetotal number of subpictures may be set to 1. In addition, width andheight information of the picture in the PPS information may be changedto the width and height information of the subpicture and extracted.

When a sub stream for one or more sub pictures is extracted from asingle stream, specific non-VCL NAL units may be included and extracted.This limitation may be for standard bitstream compatibility/conformity.

For example, if the header of the non-VCL NAL unit specifies whichsubpicture the NAL unit is associated with and an arbitrary subpictureis extracted, non-VCL NAL units associated with the subpicture may beincluded and a sub stream may be extracted. In addition, for example, ifthe header of the non-VCL NAL unit does not specify which subpicture theNAL unit is associated with, the Non-VCL NAL unit associated with PicAUincluding a subpicture to be extracted may be included and a sub streammay be extracted.

For example, if DPS, SPS NAL unit, PPS NAL unit and APS NAL unitsreferenced by the subpicture in PicAU to be extracted is extracted froma single stream, the NAL units may be included before SubAU andextracted, thereby maintaining bitstream compatibility/conformity.

In another example, if predetermined conditions are satisfied, when asub stream is extracted from a single stream, at least one of the VPSNAL unit, AUD NAL unit, EOB NAL unit or SEI NAL unit corresponding tothe extracted subpicture may not be removed.

In another example, when a sub stream is extracted from a single stream,the AUD NAL unit which does not corresponding to the extractedsubpicture may be removed.

In another example, if the AUD NAL unit is included in a single stream,aud_irap_or_gdr_flag may be set to 1 which is a first value and a substream may be extracted.

In another example, Prefix SEI NAL units related to a subpicture from asingle stream may be included before SubAU to be extracted and a substream may be extracted.

In another example, Suffix SEI NAL units related to a subpicture from asingle stream may be included after SubAU to be extracted and a substream may be extracted.

In another example, FD NAL units associated with or signaled subsequentto a subpicture extracted from a single stream may be included in a substream together and extracted. That is, only a FD NAL unit for theextracted subpicture may be extracted and FD NAL units for the remainingsubpictures may be removed.

In another example, an EOS or EOB NAL unit is present in PicAU to beextracted from a single stream, the EOS or EOB NAL unit may be includedafter SubAU and extracted. At this time, the EOS or EOB NAL unit may bealigned according to the order of NAL units of the bitstream afterSubAU. That is, when both the EOS and the EOB are present, they may bealigned in order of EOS and EOB.

In another example, when a sub stream is extracted from a single stream,an APS NAL unit which does not correspond to the extracted subpicturemay be removed.

Embodiments in which the above-described sub streams are merged into asingle stream and embodiments in which a sub stream is extracted from asingle stream are described as being performed in a coder/decoder, thesemay be performed by an apparatus including the coder/decoder or anapparatus which does not include a coder/decoder, without being limitedthereto. Here, an apparatus including a coding/decoding module may be aseparate apparatus from the coder/decoder.

For example, the separate apparatus may be referred to as a singlestream merging apparatus or a sub stream extraction apparatus. Forexample, the coder/decoder may obtain a single stream or a sub streamgenerated from a single stream merging apparatus or a sub streamextraction apparatus and perform image coding/decoding operationdescribed with reference to FIGS. 1 to 2 or perform imagecoding/decoding operation according to FIGS. 8 and 9.

For example, the coder may obtain a single stream generated from asingle stream merging apparatus and generate a sub stream. As anotherexample, the decoder may obtain a single stream generated from a singlestream merging apparatus, generate a sub stream and obtain sub pictureinformation from the sub stream. As another example, the decoder mayobtain a sub stream generated through a sub stream extraction apparatusand generate a single stream. As another example, the decoder may obtaina sub stream generated through a sub stream extraction apparatus andobtain sub picture information from the sub stream.

The above embodiments may be performed in the same method in an encoderand a decoder.

At least one or a combination of the above embodiments may be used toencode/decode a video.

A sequence of applying to above embodiment may be different between anencoder and a decoder, or the sequence applying to above embodiment maybe the same in the encoder and the decoder.

The above embodiment may be performed on each luma signal and chromasignal, or the above embodiment may be identically performed on luma andchroma signals.

A block form to which the above embodiments of the present invention areapplied may have a square form or a non-square form.

At least one of the syntax elements (flags, indices, etc.) entropy-codedin the encoder and entropy-decoded in the decoder may use at least oneof the following binarization, debinarization, entropy encoding/decodingmethods.

-   -   Method of binarization/debinarization of 0-th order Exp_Golomb        having a sign (se(v))    -   Method of binarization/debinarization of k-th order Exp_Golomb        having a sign (sek(v))    -   Method of binarization/debinarization of 0-th order Exp_Golomb        of a positive integer without a sign (ue(v))    -   Method of binarization/debinarization of k-th order Exp_Golomb        of a positive integer without a sign (uek(v))    -   Fixed-length binarization/debinarization method (f(n))    -   Truncated Rice binarization/debinarization method or or        Truncated Unary binarization/debinarization method (tu(v))    -   Truncated Binary binarization/debinarization method (tb(v))    -   Context adaptive arithmetic encoding/decoding method (ae(v))    -   Byte-unit bit string (b(8))    -   Binarization/debinarization method of an integer having a sign        (i(n))    -   Binarization/debinarization method of a positive integer without        a sign (u(n))    -   Unary binarization/debinarization method

The above embodiment of the present invention may be applied dependingon a size of at least one of a coding block, a prediction block, atransform block, a block, a current block, a coding unit, a predictionunit, a transform unit, a unit, and a current unit. Herein, the size maybe defined as a minimum size or maximum size or both so that the aboveembodiments are applied, or may be defined as a fixed size to which theabove embodiment is applied. In addition, in the above embodiments, afirst embodiment may be applied to a first size, and a second embodimentmay be applied to a second size. In other words, the above embodimentsmay be applied in combination depending on a size. In addition, theabove embodiments may be applied when a size is equal to or greater thata minimum size and equal to or smaller than a maximum size. In otherwords, the above embodiments may be applied when a block size isincluded within a certain range.

For example, the above embodiments may be applied when a size of currentblock is 8×8 or greater. For example, the above embodiments may beapplied when a size of current block is 4×4 only. For example, the aboveembodiments may be applied when a size of current block is 16×16 orsmaller. For example, the above embodiments may be applied when a sizeof current block is equal to or greater than 16×16 and equal to orsmaller than 64×64.

The above embodiments of the present invention may be applied dependingon a temporal layer. In order to identify a temporal layer to which theabove embodiments may be applied, a corresponding identifier may besignaled, and the above embodiments may be applied to a specifiedtemporal layer identified by the corresponding identifier. Herein, theidentifier may be defined as the lowest layer or the highest layer orboth to which the above embodiment may be applied, or may be defined toindicate a specific layer to which the embodiment is applied. Inaddition, a fixed temporal layer to which the embodiment is applied maybe defined.

For example, the above embodiments may be applied when a temporal layerof a current image is the lowest layer. For example, the aboveembodiments may be applied when a temporal layer identifier of a currentimage is 1. For example, the above embodiments may be applied when atemporal layer of a current image is the highest layer.

A slice type or a tile group type to which the above embodiments of thepresent invention are applied may be defined, and the above embodimentsmay be applied depending on the corresponding slice type or tile grouptype.

In the above-described embodiments, the methods are described based onthe flowcharts with a series of steps or units, but the presentinvention is not limited to the order of the steps, and rather, somesteps may be performed simultaneously or in different order with othersteps. In addition, it should be appreciated by one of ordinary skill inthe art that the steps in the flowcharts do not exclude each other andthat other steps may be added to the flowcharts or some of the steps maybe deleted from the flowcharts without influencing the scope of thepresent invention.

The embodiments include various aspects of examples. All possiblecombinations for various aspects may not be described, but those skilledin the art will be able to recognize different combinations.Accordingly, the present invention may include all replacements,modifications, and changes within the scope of the claims.

The embodiments of the present invention may be implemented in a form ofprogram instructions, which are executable by various computercomponents, and recorded in a computer-readable recording medium. Thecomputer-readable recording medium may include stand-alone or acombination of program instructions, data files, data structures, etc.The program instructions recorded in the computer-readable recordingmedium may be specially designed and constructed for the presentinvention, or well-known to a person of ordinary skilled in computersoftware technology field. Examples of the computer-readable recordingmedium include magnetic recording media such as hard disks, floppydisks, and magnetic tapes; optical data storage media such as CD-ROMs orDVD-ROMs; magneto-optimum media such as floptical disks; and hardwaredevices, such as read-only memory (ROM), random-access memory (RAM),flash memory, etc., which are particularly structured to store andimplement the program instruction. Examples of the program instructionsinclude not only a mechanical language code formatted by a compiler butalso a high level language code that may be implemented by a computerusing an interpreter. The hardware devices may be configured to beoperated by one or more software modules or vice versa to conduct theprocesses according to the present invention.

Although the present invention has been described in terms of specificitems such as detailed elements as well as the limited embodiments andthe drawings, they are only provided to help more general understandingof the invention, and the present invention is not limited to the aboveembodiments. It will be appreciated by those skilled in the art to whichthe present invention pertains that various modifications and changesmay be made from the above description.

Therefore, the spirit of the present invention shall not be limited tothe above-described embodiments, and the entire scope of the appendedclaims and their equivalents will fall within the scope and spirit ofthe invention.

INDUSTRIAL APPLICABILITY

The present invention may be used to encode or decode an image.

1. An image decoding method comprising: obtaining a single streamincluding subpicture information of a plurality of subpictures;selecting a subpicture to be extracted from among the plurality ofsubpictures; determining the single stream as a stream to be extracted;and obtaining a sub stream for the subpicture to be extracted from thestream to be extracted, by removing or using at least one piece ofsubpicture information included in the stream to be extracted.
 2. Theimage decoding method of claim 1, wherein the subpicture informationcomprises a non-video coding layer (VCL) network abstraction layer (NAL)unit and a VCL NAL unit for the plurality of subpictures.
 3. The imagedecoding method of claim 2, wherein the sub stream is obtained byremoving a VCL NAL unit for a subpicture which is not the subpicture tobe extracted.
 4. The image decoding method of claim 1, wherein thesubpicture information comprises at least one of sequence parameter set(SPS) information or picture parameter set information (PPS).
 5. Theimage decoding method of claim 4, wherein the sub stream is obtained, bysetting top left coding tree unit (CTU) coordinates of the subpicture tobe extracted are set to (0, 0).
 6. The image decoding method of claim 4,wherein the sub stream is obtained by changing information indicating atotal number of subpictures to be extracted.
 7. The image decodingmethod of claim 4, wherein the sub stream is obtained without changingat least one piece of subpicture information of the subpicture to beextracted.
 8. The image decoding method of claim 7, wherein theunchanged subpicture information comprises at least one of informationindicating whether to treat a subpicture as a picture, filteringinformation or subpicture ID information.
 9. The image decoding methodof claim 4, wherein the sub stream is obtained by removing subpictureinformation for a subpicture which is not the subpicture to beextracted.
 10. The image decoding method of claim 1, wherein thesubpicture information comprises at least one of a video parameter set(VPS) NAL unit, an end of bitstream (EOB) NAL unit, an access unitdelimiter (AUD) NAL unit or a supplemental enhancement information (SEI)NAL unit, and wherein at least one of the VPS NAL unit, the EOB NALunit, the AUD NAL unit or the SEI NAL unit is not removed from thestream to be extracted.
 11. An image encoding method comprising:obtaining a single stream including subpicture information of aplurality of subpictures; selecting a subpicture to be extracted fromamong the plurality of subpictures; determining the single stream as astream to be extracted; and obtaining a sub stream for the subpicture tobe extracted from the stream to be extracted, by removing or using atleast one piece of subpicture information included in the stream to beextracted.
 12. The image encoding method of claim 1, wherein thesubpicture information comprises a non-video coding layer (VCL) networkabstraction layer (NAL) unit and a VCL NAL unit for the plurality ofsubpictures.
 13. The image encoding method of claim 2, wherein the substream is obtained, by removing a VCL NAL unit for a sub picture whichis not the subpicture to be extracted.
 14. A computer-readable recordingmedium having stored therein a sub stream received by an image decodingapparatus and used to reconstruct a current block included in a currentpicture, the sub stream being generated by an image encoding method, theimage encoding method comprising: obtaining a single stream includingsubpicture information of a plurality of subpictures; selecting asubpicture to be extracted from among the plurality of subpictures;determining the single stream as a stream to be extracted; and obtaininga sub stream for the subpicture to be extracted from the stream to beextracted, by removing or using at least one piece of subpictureinformation included in the stream to be extracted.